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Sato, Yuki. "Quantum oscillations and charge-neutral fermions in Kondo insulator YbB₁₂." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263447.
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Bègue, Frédéric. "Isolants topologiques et magnétisme." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30392/document.
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La découverte de l'effet Hall quantique par von Klitzing en 1980 a ouvert la voie à ce qui sera connu plus tard comme la théorie topologique des bandes. Dans le cadre de cette théorie, on ne s'intéresse plus uniquement à la relation de dispersion énergétique des électrons dans les cristaux, mais aussi à l'organisation topologique de la structure de bande. Cette théorie a permis la découverte d'une nouvelle phase de la matière, représentée par les isolants topologiques. Ces isolants topologiques ont de particulier qu'ils se comportent comme des isolants normaux dans le bulk, mais présentent des états de surface conducteurs. Dans cette thèse, on s'intéresse particu- lièrement aux isolants topologiques dits Z2, pour lesquels les états de surface sont protégés par la symétrie de renversement du temps : ils ne peuvent disparaître en présence d'une perturbation qui préserve cette symétrie sans que le système ne traverse une transition de phase quantique. Pour les isolants topologiques à trois dimensions, nous proposons dans cette thèse, un critère expérimental utilisant les oscillations quantiques magnétiques, permettant d'identifier un type particulier d'isolants topologiques : les isolants topologiques forts. Pour les systèmes à deux dimensions, nous nous sommes intéressés aux phénomènes liés à la rupture de la symétrie par renversement du temps à cause de la présence d'un ordre antiferro- magnétique. Dans ce cas, la symétrie d'importance devient le renversement du temps fois une translation. Dans ce contexte, nous avons tout d'abord établi analytiquement l'expression d'un invariant topologique pour les systèmes présentant aussi la symétrie d'inversion. Nous avons ensuite adapté trois méthodes numériques normalement utilisées dans le cadre des isolants topo- logiques invariants par renversement du temps : la méthode de la phase de jonction, la méthode des centres de charge des fonctions de Wannier et la construction explicite des états de bord. Nous avons montré qu'elles permettaient de tester la nature triviale ou topologique de plusieurs modèles théoriques pour lesquelles aucune méthode n'existait, par exemple les systèmes sans symétrie d'inversionThe discovery of the quantum Hall effect by von Klitzing in 1980 paved the way for what is now known as topological band theory. In this theory, we are interested not only in the energy spectra of the electrons in crystals, but also in the topological structure of the bands. A new phase of matter was discovered thanks to this theory : the topological insulators. Topological insulators are unique in the sense that they behave like trivial insulators in the bulk, but possess metallic edge states. In this thesis, we are particularly interested in so-called Z2 topological insulators, whose edge states are protected by time reversal symmetry : they cannot disappear in the presence of a perturbation that respects this symmetry, without the system undergoing a quantum phase transition. For three-dimensional topological insulators, we propose an experimental criterion based on magnetic quantum oscillations to identify a special kind of topological insulators : the strong topological insulator. In two dimensions, we study the consequences of time reversal symmetry breaking due to anti-ferromagnetic order. In this case, the important symmetry is time reversal times a trans- lation. In this context, we first establish an analytical expression for systems that also have inversion symmetry. We then adapt three numerical methods usually employed for time reversal symmetric systems : the reconnection phase method, the Wannier charge center method and the explicit construction of edge states. We show that they are useful to probe the topology of models for which no methods were available ; such as non-centrosymmetric systems
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Semeniuk, Konstantin. "Correlated low temperature states of YFe2Ge2 and pressure metallised NiS2." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274346.
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While the free electron model can often be surprisingly successful in describing properties of solids, there are plenty of materials in which interactions between electrons are too significant to be neglected. These strongly correlated systems sometimes exhibit rather unexpected, unusual and useful phenomena, understanding of which is one of the aims of condensed matter physics. Heat capacity measurements of paramagnetic YFe$_{2}$Ge$_{2}$ give a Sommerfeld coefficient of about 100 mJ mol$^{−1}$ K$^{−2}$, which is about an order of magnitude higher than the value predicted by band structure calculations. This suggests the existence of strong electronic correlations in the compound, potentially due to proximity to an antiferromagnetic quantum critical point (QCP). Existence of the latter is also indicated by the non-Fermi liquid T$^{3/2}$ behaviour of the low temperature resistivity. Below 1.8 K a superconducting phase develops in the material, making it a rare case of a non-pnictide and non-chalcogenide iron based superconductor with the 1-2-2 structure. This thesis describes growth and study of a new generation of high quality YFe$_{2}$Ge$_{2}$ samples with residual resistance ratios reaching 200. Measurements of resistivity, heat capacity and magnetic susceptibility confirm the intrinsic and bulk character of the superconductivity, which is also argued to be of an unconventional nature. In order to test the hypothesis of the nearby QCP, resistance measurements under high pressure of up to 35 kbar have been conducted. Pressure dependence of the critical temperature of the superconductivity has been found to be rather weak. μSR measurements have been performed, but provided limited information due to sample inhomogeneity resulting in a broad distribution of the critical temperature. While the superconductivity is the result of an effective attraction between electrons, under different circumstances the electronic properties of a system can instead be dictated by the Coulomb repulsion. This is the case for another transition metal based compound NiS$_{2}$, which is a Mott insulator. Applying hydrostatic pressure of about 30 kbar brings the material across the Mott metal-insulator transition (MIT) into the metallic phase. We have used the tunnel diode oscillator (TDO) technique to measure quantum oscillations in the metallised state of NiS$_{2}$, making it possible to track the evolution of the principal Fermi surface and the associated effective mass as a function of pressure. New results are presented which access a wider pressure range than previous studies and provide strong evidence that the effective carrier mass diverges close to the Mott MIT, as expected within the Brinkman-Rice scenario and predicted in dynamical mean field theory calculations. Quantum oscillations have been measured at pressures as close to the insulating phase as 33 kbar and as high as 97 kbar. In addition to providing a valuable insight into the mechanism of the Mott MIT, this study has also demonstrated the potential of the TDO technique for studying materials at high pressures.
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Khan, Hasan. "Quantum Fluctuations Across the Superconductor-Insulator Transition." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1553188107263297.
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Tan, Hong'En. "High pressure quantum oscillation study of BiTeI and Bi2Te3." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284884.
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The work presented in this thesis investigates the behaviour of the Rashba semi-conductor BiTeI and of the topological insulator $\text{Bi}_2\text{Te}_3\,$ under pressure. Using Shubnikov-de Haas quantum oscillation measurements, the evolution of the Fermi surface of both materials was tracked as a function of pressure. At ambient pressure, two distinct quantum oscillation frequencies in BiTeI, corresponding to inner and outer Fermi surface orbits as a result of spin-splitting caused by the Rashba effect, were observed. Using a model Hamiltonian with a Rashba interaction term to model this system, experimental results were fitted to determine model parameters. Based on this model, carrier densities for the samples were calculated and there was good agreement with Hall effect measurements. The phase of the oscillations showed that both Fermi surfaces have a Berry phase of $\pi$ associated with them, consistent with theoretical predictions for a Rashba system. As pressure is applied, it was observed that the inner Fermi surface expands while the outer Fermi surface shrinks. Phase analysis of the oscillations showed deviations from the ambient pressure value, hinting at a topological transition. For $\text{Bi}_2\text{Te}_3\,$, we report the observation of two oscillation frequencies ($\sim 40$ T and $\sim 340$ T) at ambient pressures. Based on the angular dependence of the oscillation frequencies, phase analysis, and comparison against band structure from published ARPES results, it is deduced that the higher frequency oscillation corresponds to the surface state of $\text{Bi}_2\text{Te}_3$. Non-linear behaviour in the Hall measurement also suggests the presence of multiple bands, and a two-band model with parameters derived from quantum oscillation measurements is used to fit the experimental data. Under pressure, a slight decrease in the low field Hall coefficient and a new frequency appearing at $\sim 20$ kbar was observed. These may be signatures of a change in the Fermi surface of $\text{Bi}_2\text{Te}_3\,$ caused by an electronic topological transition.
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Doiron-Leyraud, Nicolas. "Quantum oscillation and high pressure studies on correlated metals." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619930.
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Mottahedeh, Roya. "Various aspects of quantum Hall effect." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306508.
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Renberg, Rasmus. "Superconductor-Insulator Quantum Phase Transitions in a Dissipative Environment." Thesis, KTH, Fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-239615.
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Hsu, Yu-Te. "Unconventional Fermi surface in insulating SmB6 and superconducting YBa2Cu3O6+x probed by high magnetic fields." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/280314.
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Fermi surface, the locus in momentum space of gapless low-energy excitations, is a concept of fundamental importance in solid state physics. Electronic properties of a material are determined by the long-lived low-energy excitations near the Fermi surface. Conventionally, Fermi surface is understood as a property exclusive to a metallic state, contoured by electronic bands crossed by the Fermi level, although there has been a continuing effort in searching for Fermi surface outside the conventional description. In this thesis, techniques developed to prepare high-quality single crystals of SmB$_6$ and YBa$_2$Cu$_3$O$_{6+x}$ (abbreviated as YBCO$_{6+x}$ hereinafter) are described. By utilising measurement techniques of exceptional sensitivity and exploring a wide range of temperatures, magnetic fields, and electrical currents, we found signatures of unconventional Fermi surfaces beyond the traditional description in these strongly correlated electronic systems. SmB$_6$ is a classic example of Kondo insulators whose insulating behaviour arises due to strong correlation between the itinerant $d$-electrons and localised $f$-electrons. The peculiar resistivity plateau onsets below 4 K has been a decades-long puzzle whose origin has been recently proposed as the manifestation of topological conducting surface states. We found that the insulating behaviour in electrical transport is robust against magnetic fields up to 45 T, while prominent quantum oscillations in magnetisation are observed above 10 T. Angular dependence of the quantum oscillations revealed a three-dimensional characteristics with an absolute amplitude consistent with a bulk origin, and temperature dependence showed a surprising departure from the conventional Lifshitz-Kosevich formalism. Complementary thermodynamic measurements showed results consistent with a Fermi surface originating from neutral itinerant low-energy excitations at low temperatures. Theoretical proposals of the unconventional ground state uncovered by our measurements in SmB$_6$ are discussed. YBCO$_{6+x}$ is a high-temperature superconductor with a maximum $T_{\rm c}$ of 93.5 K and the cleanest member in the family of copper-oxide, or {\it cuprate}, superconductors. The correct description of electronic ground state in the enigmatic pseudogap regime, where the antinodal density of states are suppressed below a characteristic temperature $T^*$ above $T_{\rm c}$, has been a subject of active debates. While the quantum oscillations observed in underdoped YBCO$_{6+x}$ have been predominately interpreted as a property of the normal state where the superconducting parameter is completely suppressed at $\approx$ 23 T, we made the discovery that YBCO$_{6.55}$ exhibits zero resistivity up to 45 T when a low electrical current is used, consistent with the observation of a hysteresis loop in magnetisation. Quantum oscillations in the underdoped YBCO$_{6+x}$ are thus seen to coexist with $d$-wave superconductivity. Characteristics of the quantum oscillations are consistent with an isolated Fermi pocket reconstructed by a charge density wave order parameter and unaccompanied by significant background density of states, suggesting the antinodal density of states is completely gapped out by a strong order parameter involving pairing correlations, potentially in addition to the other order parameters. Transport measurements performed over a wide doping range show signatures consistent with pairing correlations that persist up to the pseudogap temperature $T^*$. The surprising observation of quantum oscillations in insulating SmB$_6$ and superconducting YBCO$_{6+x}$ demonstrates a possible new paradigm of a Fermi surface without a conventional Fermi liquid. A new theoretical framework outside the realm of Fermi liquid theory may be needed to discuss the physics in these strongly correlated materials with enticing electronic properties.
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Li, Li. "Study of Metal-Insulator-Metal Diodes for Photodetection." University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1367319217.
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Schroeder, Brett. "Surface modification enhanced semiconductor-on-insulator heteroepitaxy /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/9808.
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Lam, Jennifer. "The nature of the metal-insulator transition in SiGe quantum wells." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20977.pdf.
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Piekarek, Mateusz. "High-extinction ratio optical filtering for silicon-on-insulator quantum photonics platform." Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715763.
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Lam, Jennifer Eleanor. "The nature of the metal-insulator transition in silicon germanide quantum wells." Thesis, University of Ottawa (Canada), 1997. http://hdl.handle.net/10393/4399.
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A study of the temperature dependence of the resistivity of gated SiGe quantum well structures has revealed a metal-insulator transition as a function of carrier density at zero magnetic field. Although early scaling theories (Abrahams et al., 1979) have argued against the existence of a metal-insulator transition at zero temperature in infinite 2D and 1D systems, more recent theoretical results using a random set of two-dimensional point potentials have shown that such a transition is allowed in two dimensions (Az'bel, 1992). Mounting experimental evidence for such a transition in 2D systems with short range scattering has accumulated in both semiconducting and superconducting structures (Kravchenko et al., 1995, and others). Pseudomorphic, CVD-grown p-type Si/Si$\sb{0.87}$Ge$\sb{0.13}$/Si quantum wells of various widths (65-200 A) have been studied. The samples were gated using a Ti-Au Schottky gate to allow for carrier density variation. Measurement of the transport to quantum lifetime ratio indicates that the transport is dominated by short range scattering. In the temperature range from 400 mK - 4.2 K, the temperature dependence shows a transition from a metallic phase in the high density regime to an insulating phase in the low density regime with a transition boundary close to 2.2 $\times$ 10$\sp $ cm$\sp{-2}$. The scaling properties of the observed metal-insulator transition will be discussed, and compared to previous scaling results from silicon MOSFETs. Below 400 mK, the onset of another transition is accompanied by a sharp drop in resistivity with temperature followed by a monotonic decrease in resistivity below 115 mK. The phase diagram was explored using temperature and density dependences of the current-voltage characteristics.
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Ziegler, Johannes [Verfasser], and Dieter [Akademischer Betreuer] Weiss. "Quantum transport in HgTe topological insulator nanostructures / Johannes Ziegler ; Betreuer: Dieter Weiss." Regensburg : Universitätsbibliothek Regensburg, 2019. http://d-nb.info/1180719573/34.
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Francheteau, Anaïs. "Superconducting silicon on insulator and silicide-based superconducting MOSFET for quantum technologies." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY092/document.
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L'introduction de la supraconductivité dans des structures de type MOSFET en silicium ouvre de nouvelles perspectives dans la recherche en physique. Dans cette thèse, on s'intéresse aux propriétés de transport électronique au sein d'un MOSFET fabriqué avec des sources et drains supraconducteurs. Afin de garantir la reproductibilité de ces dispositifs, il est important d'intégrer des matériaux supraconducteurs compatibles avec la technologie CMOS exploitant la technologie silicium qui a pour énorme avantage d'être véritablement fiable et mature. L'idée fondamentale est de réaliser un nouveau type de circuit supraconducteur avec une géométrie de type transistor dans lequel un supracourant non dissipatif circulant au sein du dispositif, de la source vers le drain, serait modulé par une tension de grille : un JOFET. Une perspective importante est la réalisation d'un qubit supraconducteur grâce à une technologie parfaitement reproductible et mature. Cependant, à très basse température et avec la diminution de la taille des dispositifs, deux phénomènes a priori antagonistes entrent en compétition, à savoir la supraconductivité qui implique un grand nombre d'électrons condensés dans le même état quantique macroscopique et l'interaction Coulombienne qui décrit des processus de transport à une particule. L'intérêt de l'étude est donc de réaliser de tels transistors afin de mieux comprendre comment ce genre de dispositif hybride peut s'adapter à des propriétés opposées. Dans cette thèse, j'ai étudié deux façons d'introduire la supraconductivité dans nos dispositifs. La première option est de réaliser des sources et drains en silicium rendus supraconducteurs par dopage en bore et recuit laser effectué grâce à des techniques de dopage hors-équilibre robustes et bien maîtrisées. Même si la supraconductivité du silicium très fortement dopé en bore est connue depuis 2006 et son état supraconducteur a été très bien caractérisé sur des couches bidimensionnelles, la supraconductivité du SOI, qui est le substrat initial à la base de certains transistors, n'a jamais encore été testée et étudiée. L'objectif est de pouvoir adapter ces techniques de dopage au SOI afin de le rendre supraconducteur et de pouvoir l'intégrer par la suite dans des dispositifs de type MOSFET. La seconde option considérée est la réalisation de source et drain à base de siliciures supraconducteurs tel que le PtSi. Ce siliciure est intéressant du point de vue de sa température critique relativement haute de 1K. D'un point de vue technologique, les MOSFETs à barrière Schottky présentant des contacts en PtSi supraconducteur ont été élaborés au CEA/LETI. Les mesures à très basse température au sein d'un cryostat à dilution ont mis en évidence cette compétition entre la supraconductivité et les effets d'interaction Coulombienne et ont également révélé la supraconductivité dans le MOSFET comportant des contacts en PtSi grâce notamment à l'observation du gap induit dans le dispositifSuperconducting transport through a silicon MOSFET can open up many new possibilities ranging from fundamental research to industrial applications. In this thesis, we investigate the electric transport properties of a MOSFET built with superconducting source and drain contacts. Due to their advantages in terms of scalability and reproducibility, we want to integrate superconducting materials compatible with CMOS technology, thus exploiting the reliable and mature silicon technology. The idea is to realize a new type of superconducting circuits in a transistor geometry in which a non-dissipative supercurrent flowing through the device from source to drain will be modulated by a gate: a JOFET. One important outcome is the realization of superconducting qubits in a perfectly reproducible and mature technology. However, at low temperature and with the reduction of the size of the devices, two antagonistic phenomena appear. The dissipation-free transport of Cooper pairs competes with lossy single-particle processes due to Coulomb interactions. The goal is to understand how these two conflicting properties manifest in such hybrid devices. In this thesis, I studied two different ways of introducing superconductivity in the devices. We deployed a high boron doping and a laser annealing provided by well-controlled out-of-equilibrium doping techniques to make the silicon superconducting. Although highly boron-doped silicon has been known to be superconducting since 2006, superconductivity of SOI, the basic brick of some transistors, was never tested before. We aim at adapting those doping techniques on SOI in order to make it superconducting and to integrate it in transistor-like devices. In a second project, we study source and drain contacts fabricated with superconducting silicides such as PtSi. Such Schottky barrier MOSFETs with superconducting PtSi contacts are elaborated at the CEA/LETI. Measurements at very low temperature revealed the competition between superconductivity and Coulomb interactions and moreover, have brought evidence of superconductivity in PtSi based silicon Schottky barrier MOSFET
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Di, Mauro Marco. "Flavor mixing in quantum field theory and quantum information." Doctoral thesis, Universita degli studi di Salerno, 2011. http://hdl.handle.net/10556/194.
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2009 - 2010After reviewing the formalism for describing flavor mixing, both in Quantum Mechanics and Quantum Field Theory, some consequences along three different directions are studied. First, it is proposed that flavor mixing can be a viable candidate for spontaneous supersymmetry breaking, due to the nontrivial vacuum structure induced by it. After the statement of the conjecture, an explicit proof in a simple case is given. Second, the properties of flavor states as entangled states both in QM and QFT are studied. By interpreting such states as multipartite mode–entangled states, both the correlation content and the decoherence effects are studied. Third, a possible new interpretation of flavor mixing as induced by an external vector field is proposed, and it is shown how this solves some problems of the usual formalism in connection with Lorentz and Poincar´e violation. Some phenomenological consequences of this picture are pointed out, as well as some intriguing physical interpretations. [edited by author]
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Hussain, Mallik Mohd Raihan. "Effective Nonlinear Susceptibilities of Metal-Insulator and Metal-Insulator-Metal Nanolayered Structures." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1591207594352716.
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Boukahil, Mounir. "Quantum criticality and Fermisurface instabilities investigation by pressure and quantum oscillation measurements on Ce and Ybbased heavy fermion compounds." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY090/document.
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L'auteur n'a pas fourni de résumé en françaisThe superconductivity had been thought to be incompatible with the magnetism, because the former originates from the weak attractive leading to the formation of Cooper pairs, whereas the latter is based on the strong Coulomb repulsive force, leading also to strong electronic correlations. Unconventional superconductors,which include heavy fermion systems, high-Tc cuprates, organic superconductors, and iron-pnictides, is a major topic of condensed matter physics. In all these systems, it has been understood that magnetism can even plays an important role for the pairing mechanism, so that both phenomena can coexist and even favour each other.Our target is on heavy fermion systems, namely uranium and rare earth compounds, where the 5f or 4f electrons which have a dual nature (itinerant/localized), play an important role. More precisely, we will focus on the ferromagnetic superconductors and their quantum criticality. In this field, new materials open new frontiers of research. The student will participate in this stream. He will learn and develop the fundamental crystal growth techniques, such as Czochralski, flux, and Bridgeman method. Since high quality single crystals are essential to elucidate the superconducting properties, a lot of efforts will be devoted to improve the quality of the samples. The next target is the quantum oscillation measurements, which allow a detailed microscopic observation of the heavy electronic state and of the topology of the Fermi surface. They require both very low temperature and high fields, like the study of the field induced superconducting phases in these compounds (like URhGe or UCoGe). The student will perform the measurements under extreme conditions, namely high fields up to 15T in SPSMS, or up to 30T in LNCMI, at low temperatures down to 30 mK, and high pressure up to 3 GPa.From the educational point of view, it is ideal that the student starts to synthesize a material, characterizes it, performs the low temperature measurements by him/herself throughout the PhD period, and get used to the exciting measurements under extreme conditions in a large scale facility like the LNCMI. Such a wide spectrum is rather rare in Europe, but our group („SPSMS/LNCMI) can provide such a unique opportunity, helping the student to become an independent researcher. It should be noted that the experiments in SPSMS and LNCMI are quite complementary each other. For quantum oscillation study, high fields, low temperatures and high quality singles are inevitably important. In general, the precise measurements at high fields up to 15T would be enough in order to determine the Fermi surface topology and the effective mass, which canbe done in SPSMS. However, the specific case, such as Lifshitz transition, field induced quantum critical phenomena, requires higher fields than 15T, which can be achieved by the resistive magnet in LNCMI.This project is supported by the ANR (CORMAT, SINUS) and the ERC starting grant “NewHeavyFermion”.Recently in SPSMS we purchased a top-loading dilution refrigerator for the quantum oscillation measurements, and started the installation. By the end of this summer, hopefully we detect the first de Haas-van Alphen signal at high fields up to 15T and at temperatures down to 30mK. Furthermore, we started to install the flux crystal growth equipment this month, involving the reconstruction of the room for the safe treatment of uranium compounds
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Qiu, Lei. "Exploring 2D Metal-Insulator Transition in p-GaAs Quantum Well with High rs." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1386337954.
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Bonneau, Damien. "Integrated quantum photonics at telecommunication wavelength in silicon-on-insulator and lithium niobate platforms." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664624.
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Photonic quantum technologies are a promising approach to implement quantum information tasks including physically secured communication, efficient simulation of quantum systems, and could ultimately lead to the realisation of a full scale quantum computer. Integrated photonics have been successfully used to expand the scope of quantum optics experiments, unlocking the capability to perform more and more complex quantum tasks. The current effort points towards the integration of all the components in a single monolithic chip including single photon sources, passive circuits, fast phase-modulators, single photon detectors and electronics. Following this goal, we present technological steps towards further integration. We first show fast manipulation of single and two-photon states in an integrated lithium niobate circuit. We then move to the silicon-on-insulator platform providing orders of magnitude more compact circuits. We demonstrate the operation of several key components in the quantum regime, including quantum interference in a passive integrated multimode coupler, manipulation of quantum states using a reconfigurable phase-shifter in a Mach-Zehnder interferometer, and on-chip production of photon pairs. Engineering considerations are discussed for different components, including a study of the optimal parameter space for resonant photon pair sources. We then demonstrate the combined operation in a single chip of two photon pair sources together with passive circuitry and a phase-shifter, and show high visibility on the resulting quantum interference fringes. Then, considering state of the art technologies, including results from this work, we study several multiplexed schemes for implementing a crucially missing building block so far: a near-deterministic single photon source.
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Tenasini, Giulia. "Quantum transport in monolayer WTe2." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14897/.
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Il ditellurio di tungsteno (WTe2) appartiene alla classe dei dicalcogenuri di metalli di transizione (TMDs), che rappresentano attualmente i materiali più promettenti, insieme al grafene, nel campo di ricerca dei cristalli bidimensionali (2D). Grazie ad una caratteristica struttura stratificata, con differenti piani atomici legati da forze di van der Waals, mediante esfoliazione è possibile isolare strati di spessore quasi-atomico di TMDs, detti “monostrati”, con proprietà spesso molto diverse dal materiale bulk originario. Il WTe2 nella sua forma a monostrato, è stato recentemente oggetto di interesse scientifico, in quanto teoricamente predetto essere un isolante topologico (TI) bidimensionale. Un TI è un materiale che internamente si comporta come un isolante elettrico ma che sulla superficie manifesta stati conduttivi. Lo scopo di questa tesi è studiare le proprietà si trasporto di monostrati di WTe2 in micro-dispositivi realizzati con opportune tecniche di nanofabbricazione. L'ossidazione della superficie esterna del WTe2, dovuta ad una non-perfetta stabilità in aria, influenza significativamente il trasporto elettronico in cristalli costituiti da pochi strati atomici ed è causa di una transizione metallo-isolante. Una possibile soluzione per evitare la degradazione del materiale consiste nell' “incapsulamento” di un monostrato di WTe2 fra materiali 2D chimicamente inerti, come il nitruro di boro esagonale. A tale proposito, si è sviluppata una tecnica di “trasferimento” che permette di sollevare e allineare con precisione micrometrica strati di spessore atomico di differenti materiali, assemblando eterostrutture di van der Waals. Campioni selezionati sono studiati mediante misure di magneto-transporto a bassa temperatura (fino a 0.250 K). I dati analizzati evidenziano l'esistenza di un gap di energia in monostrati di WTe2 e la presenza di una corrente localizzata ai bordi del sistema, coerentemente con l'ipotesi di un isolante topologico 2D.
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Perez, Barraza Julia Isabel. "Ultrasmall silicon quantum dots for the realization of a spin qubit." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708003.
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Watson, Deborah Lee. "Quantum interference effects in the magnetoresistance of semiconductor structures near the metal to insulator transition." Thesis, University of Exeter, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286547.
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O'Neal, Jared. "A Numerical Study of a Disorder-driven 2D Mott Insulator-to-Metal Quantum Phase Transition." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492701913534985.
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Schönle, Joachim. "Quantum transport studies for spintronics implementation : from supramolecular carbon nanotube systems to topological crystalline insulator." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY022/document.
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L'électronique moléculaire est l'un des domaines les plus intrigants de la recherche moderne. Ce domaine pourrait produire un système de construction modulaire et évolutif pour des applications spintroniques à l'échelle nanométrique. Un exemple particulièrement prometteur est celui des aimants à une seule molécule, qui se sont déjà avérés être appropriés pour des la réalisation de spin valve et de qubit de spin. L'un des plus grands défis du domaine est l'intégration de ces objets de taille nanométrique dans des circuits complexes afin de permettre la détection et la manipulation d'états de spin moléculaires. Comme l'ont montré ces dernières années le groupe NanoSpin, les nanotubes de carbone (CNTs) peuvent servir de support pour les aimants à une seule molécule, en combinant les caractéristiques des deux constituants.Une pierre angulaire de ce projet de thèse a donc été le développement d'une technique de fabrication fiable pour des dispositifs de CNTs de haute qualité, contrôlables par de multiples électrodes de grille locales afin de permettre le contrôle local des systèmes hybrides moléculaires. Un procédé basé sur la fabrication conventionnelle à un substrat a été développé à partir de zéro, pour lequel l'optimisation de la conception des échantillons, les techniques de lithographie et de dépôt ainsi que les choix de matériaux ont dû être soigneusement incorporés afin de respecter les restrictions imposées par les conditions de croissance. Nous avons d'abord réussi à produire des échantillons CNT propres, permettant de mettre en évidence une configuration à double boite quantique, tout en ajustant des caractéristiques de type p à n. Les segments créés de cette manière peuvent être contrôlés de manière stable sur toute la longueur du dispositif et devraient donc constituer une base appropriée pour l'étude de la physique moléculaire.La matière topologique non triviale constitue une plate-forme séduisante pour étudier à la fois les principes fondamentaux et les applications possibles de la spintronique au calcul quantique. Les isolants cristallins topologiques, avec tellurure d'étain (SnTe) comme exemple principal, représentent un nouvel état au sein de ce zoo des matériaux topologiques 3D. Peu de temps après les premières réalisations expérimentales, des suggestions ont été faites sur la possibilité d’un type de supraconductivité non conventionnelle hébergé à l'interface entre la matière topologique et les supraconducteurs classiques. Les implications possibles de ces systèmes comprennent l'appariement de Cooper avec une quantité de mouvement finie dans la phase FFLO ou l’ordinateur quantique topologique, basé sur des excitations particulières, appelé quasi-particule Majorana.Ce projet de thèse visait à participer à l'enquête sur les signes de supraconductivité non conventionnelle dans SnTe. Les expériences de transport sur des couches pures dans les géométries de la barre de Hall et des dispositifs hybrides supraconducteurs, réalisés à la fois comme jonctions Josephson et SQUID, sont discutés. Un couplage étonnamment fort de SnTe au supraconducteur a été trouvé et dépendances de la supraconductivité sur les géométries des échantillons, la température et le champ magnétique ont été étudiées. La relation courant-phase a été analysée dans la limite d’effets cinétiques forts. Le couplage électrostatique et l'exposition à des micro-ondes ont été explorée, mais la physique prédominante dans de telles configurations s'est avéré être de type purement conventionnel, soulignant l’importance des améliorations sur le côté matériaux.Des mesures de champ magnétique dans le plan ont donné lieu à la signature d’un φ0-SQUID avec des transitions 0-π accordables, fournissant des preuves de possibles de transitions contrôlées de la supraconductivité triviale aux régimes de couplage non conventionnels dans SnTeMolecular electronics is one of the most intriguing fields of modern research, which could bring forth a modular and scalable building system for nanoscale spintronics applications. A particularly promising example are single-molecule magnets, which have already successfully shown to be suitable for spin valve or spin qubit operations. One of the biggest challenges of the field is the integration of these nanometer-sized objects in complex circuits in order to allow for detection and manipulation of moleculear spin states. As shown in recent years by the NanoSpin group, carbon nanotubes (CNTs) can serve as such type of carrier for the single-molecule magnets, combining features of both constituents.A corner stone of this thesis project was hence the development of a dependable fabrication technique for high-quality CNT devices, controllable by multiple local gate electrodes in order to enable local control of molecular hybrid systems. A process based on conventional one-chip fabrication was developed from scratch, for which optimization of sample design, lithography and deposition techniques as well as material choices had to be carefully incorporated, in order to accomodate the restrictions imposed by the CNT growth conditions on the prevention of leakage currents. We succeeded in producing clean CNT devices, which could support a double dot configuration, tunable from p- to n-type characteristics. The segments created in this way can be stabily controlled over the entire device length and should hence provide a suitable backbone to study molecular physics.Topological matter constitutes an enticing platform to investigate both fundamental principles as well as possible applications from spintronics to quantum computation. Topological crystalline insulators, with tin telluride ( SnTe ) as a prime example, represent a new state of matter within this zoo of 3D topological materials. Soon after first experimental realizations, suggestions were made about the possibility of an unconventional type of superconductivity hosted at the interface between topological matter and conventional superconductors. Possible implications of such systems include Cooper pairing with finite momentum, the FFLO phase, or topological quantum computing, based on peculiar excitations, called Majorana bound states.This thesis project aimed to participate in the investigation of signs of unconventional superconductivity in SnTe . Transport experiments on bare films in Hall bar geometries and superconducting hybrid devices, realized as both Josephson junctions and SQUIDs, are discussed. A surprisingly strong coupling of SnTe to Ta superconductor was found and dependencies of superconductivity on sample geometries, temperature and magnetic field were investigated. The current-phase relation was analyzed in the limit of strong kinetic effects. Electrostatic gating and rf exposure was explored, but predominant physics in such configurations turned out to be of purely conventional type, pointing out the importance of improvements on the material side.In-plane magnetic field measurements gave rise to the manifestation of ϕ0-SQUIDs with tunable 0−π-transitions, providing evidence for possible controlled transitions from trivial superconductivity to unconventional coupling regimes in SnTe
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Hussain, Mallik Mohd Raihan. "Nonlinear Electromagnetic Radiation from Metal-Insulator-Metal Tunnel Junctions." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1490823061190116.
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Clarke, Warrick Robin Physics Faculty of Science UNSW. "Quantum interaction phenomena in p-GaAs microelectronic devices." Awarded by:University of New South Wales. School of Physics, 2006. http://handle.unsw.edu.au/1959.4/32259.
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In this dissertation, we study properties of quantum interaction phenomena in two-dimensional (2D) and one-dimensional (1D) electronic systems in p-GaAs micro- and nano-scale devices. We present low-temperature magneto-transport data from three forms of low-dimensional systems 1) 2D hole systems: in order to study interaction contributions to the metallic behavior of 2D systems 2) Bilayer hole systems: in order to study the many body, bilayer quantum Hall state at nu = 1 3) 1D hole systems: for the study of the anomalous conductance plateau G = 0.7 ???? 2e2/h The work is divided into five experimental studies aimed at either directly exploring the properties of the above three interaction phenomena or the development of novel device structures that exploit the strong particle-particle interactions found in p-GaAs for the study of many body phenomena. Firstly, we demonstrate a novel semiconductor-insulator-semiconductor field effect transistor (SISFET), designed specifically to induced 2D hole systems at a ????normal???? AlGaAs-on-GaAs heterojunction. The novel SISFETs feature in our studies of the metallic behavior in 2D systems in which we examine temperature corrections to ????xx(T) and ????xy(T) in short- and long-range disorder potentials. Next, we shift focus to bilayer hole systems and the many body quantum Hall states that form a nu = 1 in the presence of strong interlayer interactions. We explore the evolution of this quantum Hall state as the relative densities in the layers is imbalanced while the total density is kept constant. Finally, we demonstrate a novel p-type quantum point contact device that produce the most stable and robust current quantization in a p-type 1D systems to date, allowing us to observed for the first time the 0.7 structure in a p-type device.
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VELLEI, ANTONIO. "Silicon-on-insulator nanowires as spintronic device for quantum computing: design, processing, fabrication and electrical characterization." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2011. http://hdl.handle.net/10281/20213.
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In semiconductor industries, the passage from traditional CMOS toward SOI technology has fruitfully helped for eliminating most of the detrimental substrate effects connected with leakage current and parasitic effect present in devices fabricated according to CMOS technology. It can be argued how SOI technology emphasizes the real capabilities of low dimensional systems. Nanowires (NWs) are basilar structures which have two quantum confined directions which, if opportunely scaled down, are expected to give rise to quantistic confinement, while still leaving one unconfined direction for electrical conduction. Such basic structure can then be exploited to get an electrical tool for the readout of phenomena which obeys to quantum physics laws. The spin-state of the paramagnetic centers located inside the n-type doped SOI-NWs can be then thought as a
potential candidate for accessing to the Quantum Information Processing. Silicon NWs were fabricated in SOI technology by exploiting a top-down approach, that is
the Electron Beam Lithography (EBL). A custom EBL system provided by University of Pisa was used for this purpose. Both the EBL technology and all the needed process steps (thermal treatments, chemical processing, metal patterning, etc.) have been set-up in MDM by the thesis author in order to finalize the fabrication of SOI-NWs. All process steps were integrated for fabricating of devices with three different layouts. The smallest patterning structures were in the range of 50±5nm for wired structures. The structures fabricated for the electrical tests (devices) had trapezoidal section whose typical dimension was below 100 nm. The layouts of these device were designed in order to provide the
readout of the spin resonance signal coming out from the paramagnetic centres located both in the bulk and at the Si-SiO2 interfaces of the NWs conductive channel. Current-Voltage measurements were carried on at different temperatures in order to extract
the metal-semiconductor junction parameters and to identify the conduction mechanism ruling the carrier motion in different temperature ranges. Electrically Detected Magnetic Resonance (EDMR)measurements were performed at low temperature in order to test, as already mentioned, the capability of such devices for providing the readout of the spin-state. The EDMR test results were quite good: the highest sensitivity reached was of 102 centres. Despite of many efforts have to be carried on in this matter, EDMR has demonstrated to be a suitable technique for getting the readout of donor electron spin state inside SOI-NWs.
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Rosenbach, Daniel [Verfasser], Daniel [Akademischer Betreuer] Schäpers, and Markus [Akademischer Betreuer] Morgenstern. "Quantum transport and induced superconductivity in selectively deposited topological insulator devices / Daniel Rosenbach ; Daniel Schäpers, Markus Morgenstern." Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/1240480407/34.
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Ratnadurai, Rudraskandan. "Development of a Reliable Metal-Insulator-Metal Bilayer Tunnel Junction for Wideband Detectors." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4394.
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Detectors and sensors are an integral part of modern electronics and are crucial to highly sensitive applications. Metal-Insulator-Metal (MIM) tunnel junctions have been explored for the past five decades and are still being investigated due to its wide use of applications such as mixers, capacitors, detectors, rectifiers and energy conversion devices. In this research, various designs of thin film based tunnel junctions have been investigated and the optimum one picked for the purpose of a wide band detector up to 10GHz based on their sensitivities. A modified design with an isolation layer incorporating a self-aligning method to increase fabrication throughput was developed. A mask for the reliability testing of multiple devices with different areas was also developed. Nickel Oxide based insulators with different stoichiometries have been incorporated in the fabrication of the device to identify which stoichiometry gives the best performance for high frequency applications. Nickel Oxide (NiO), Zinc Oxide (ZnO) and the combination of the two have been deposited using reactive sputtering and investigated as insulator materials. The bilayer devices showed increased sensitivities at lower turn on voltages and very good efficiencies at 100MHz and 1GHz. Although, the MIM device provides a simple structure, some of the critical parameters required to quantify the device functionality are still being explored. Based on the parameters, a criterion was developed to help engineer a tunnel device for a desired detectivity.
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Repellin, Cécile. "Numerical study of fractional topological insulators." Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0028/document.
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Les isolants topologiques sont des isolants qui ne peuvent être différenciés des isolants atomiques que par une grandeur physique non locale appelée invariant topologique. L'effet Hall quantique et son équivalent sans champ magnétique l'isolant de Chern sont des exemples d'isolants topologiques. En présence d'interactions fortes, des excitations exotiques appelées anyons peuvent apparaître dans les isolants topologiques. L'effet Hall quantique fractionnaire (EHQF) est la seule réalisation expérimentale connue de ces phases. Dans ce manuscrit, nous étudions numériquement les conditions d'émergence de différents isolants topologiques fractionnaires. Nous nous concentrons d'abord sur l'étude de l'EHQF sur le tore. Nous introduisons une méthode de construction projective des états EHQF les plus exotiques complémentaire par rapport aux méthodes existantes. Nous étudions les excitations de basse énergie sur le tore de deux états EHQF, les états de Laughlin et de Moore-Read. Nous proposons des fonctions d'onde pour les décrire, et vérifions leur validité numériquement. Grâce à cette description, nous caractérisons les excitations de basse énergie de l'état de Laughlin dans les isolants de Chern. Nous démontrons également la stabilité d'autres états de l'EHQF dans les isolants de Chern, tels que les états de fermions composites, Halperin et NASS. Nous explorons ensuite des phases fractionnaires sans équivallent dans la physique de l'EHQF, d'abord en choisissant un modèle dont l'invariant topologique a une valeur plus élevée, puis en imposant au système la conservation de la symétrie par renversement du temps, ce qui modifie la nature de l'invariant topologiqueTopological insulators are band insulators which are fundamentally different from atomic insulators. Only a non-local quantity called topological invariant can distinguish these two phases. The quantum Hall effect is the first example of a topological insulator, but the same phase can arise in the absence of a magnetic field, and is called a Chern insulator. In the presence of strong interactions, topological insulators may host exotic excitations called anyons. The fractional quantum Hall effect is the only experimentally realized example of such phase. In this manuscript, we study the conditions of emergence of different types of fractional topological insulators, using numerical simulations. We first look at the fractional quantum Hall effect on the torus. We introduce a new projective construction of exotic quantum Hall states that complements the existing construction. We study the low energy excitations on the torus of two of the most emblematic quantum Hall states, the Laughlin and Moore-Read states. We propose and validate model wave functions to describe them. We apply this knowledge to characterize the excitations of the Laughlin state in Chern insulators. We show the stability of other fractional quantum Hall states in Chern insulators, the composite fermion, Halperin and NASS states. We explore the physics of fractional phases with no equivalent in a quantum Hall system, using two different strategies: first by choosing a model with a higher value of the topological invariant, second by adding time-reversal symmetry, which changes the nature of the topological invariant
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Ellis, Jason Keith. "Emergent Phenomena in Classical and Quantum Systems: Cellular Dynamics in E. coli and Spin-Polarization in Fermi Superfluids." [Kent, Ohio] : Kent State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1256932939.
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Lam, Ping Koy, and Ping Lam@anu edu au. "Applications of Quantum Electro-Optic Control and Squeezed Light." The Australian National University. Faculty of Science, 1999. http://thesis.anu.edu.au./public/adt-ANU20030611.170800.
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In this thesis, we report the observations of optical squeezing from second harmonic generation (SHG), optical parametric oscillation (OPO) and optical parametric amplification (OPA). Demonstrations and proposals of applications involving the squeezed light and electro-optic control loops are presented.
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In our SHG setup, we report the observation of 2.1 dB of intensity squeezing on the second harmonic (SH) output. Investigations into the system show that the squeezing performance of a SHG system is critically affected by the pump noise and a modular theory of noise propagation is developed to describe and quantify this effect. Our experimental data has also shown that in a low-loss SHG system, intra-cavity nondegenerate OPO modes can simultaneously occur. This competition of nonlinear processes leads to the optical clamping of the SH output power and in general can degrade the SH squeezing. We model this competition and show that it imposes a limit to the observable SH squeezing. Proposals for minimizing the effect of competition are presented.
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In our OPO setup, we report the observation of 7.1 dB of vacuum squeezing and more than 4 dB of intensity squeezing when the OPO is operating as a parametric amplifier. We present the design criteria and discuss the limits to the observable squeezing from the OPO.We attribute the large amount of squeezing obtained in our experiment to the high escape efficiency of the OPO. The effect of phase jitter on the squeezing of the vacuum state is modeled.
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The quantum noise performance of an electro-optic feedforward control loop is investigated. With classical coherent inputs, we demonstrate that vacuum fluctuations introduced at the beam splitter of the control loop can be completely cancelled by an optimum amount of positive feedforward. The cancellation of vacuum fluctuations leads to the possibility of noiseless signal amplification with the feedforward loop. Comparison shows that the feedforward amplifier is superior or at least comparable in performance with other noiseless amplification schemes. When combined with an injection-locked non-planar ring Nd:YAG laser, we demonstrate that signal and power amplifications can both be noiseless and independently variable.
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Using squeezed inputs to the feedforward control loop, we demonstrate that information carrying squeezed states can be made robust to large downstream transmission losses via a noiseless signal amplification. We show that the combination of a squeezed vacuum meter input and a feedforward loop is a quantum nondemolition (QND) device, with the feedforward loop providing an additional improvement on the transfer of signal. In general, the use of a squeezed vacuum meter input and an electro-optic feedforward loop can provide pre- and post- enhancements to many existing QND schemes.
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Finally, we proposed that the quantum teleportation of a continuous-wave optical state can be achieved using a pair of phase and amplitude electro-optic feedforward loops with two orthogonal quadrature squeezed inputs. The signal transfer and quantum correlation of the teleported optical state are analysed. We show that a two dimensional diagram, similar to the QND figures of merits, can be used to quantify the performance of a teleporter.
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Konishi, Hideki. "Collisional stability of localized metastable ytterbium atoms immersed in a Fermi sea of lithium." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225386.
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Kessel, Maximilian [Verfasser], Hartmut [Gutachter] Buhmann, and Grzegorz [Gutachter] Karczewski. "HgTe shells on CdTe nanowires: A low-dimensional topological insulator from crystal growth to quantum transport / Maximilian Kessel ; Gutachter: Hartmut Buhmann, Grzegorz Karczewski." Würzburg : Universität Würzburg, 2017. http://d-nb.info/1132995868/34.
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Liang, Dong. "Semiconductor Nanowires: Synthesis and Quantum Transport." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1327641946.
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Forino, Paola Caterina. "Nuclear magnetic resonance study of the electron doped Dirac-Mott Insulator double perovskite Ba2Na(1-x)CaxOsO6." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Find full textAbstract:
Osmium-based materials exhibit unconventional magnetism due to the interplay between spin orbit coupling and strong electronic correlations.
In this thesis we investigate for the first time the effect of charge doping on the Dirac Mott insulator double perovskites Ba2Na(1-x)CaxOsO6 by using Nuclear Magnetic Resonance technique. We study in details the evolution of the magnetic phase diagram as a function of doping and applied magnetic field.
The system rapidly evolves from a canted to a collinear antiferromagnetic ground state with a monotonic increase of the magnetic transition temperature. Furthermore, the system remains insulating in the whole range of doping, despite the injection of extra electrons. This indicates that the Dirac-Mott insulating state of this material is unusually robust.
In particular, the results show an unexpected thermally activated charge dynamics which suggests the presence of polarons dominating the high temperature excitations of this Dirac-Mott insulator.
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Dauphin, Alexandre. "Cold atom quantum simulation of topological phases of matter." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209076.
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L'étude des phases de la matière est d'un intérêt fondamental en physique. La théorie de Landau, qui est le "modèle standard" des transitions de phases, caractérise les phases de la matière en termes des brisures de symétrie, décrites par un paramètre d'ordre local. Cette théorie a permis la description de phénomènes remarquables tels que la condensation de Bose-Einstein, la supraconductivité et la superfluidité.Il existe cependant des phases qui échappent à la description de Landau. Il s'agit des phases quantiques topologiques. Celles-ci constituent un nouveau paradigme et sont caractérisées par un ordre global défini par un invariant topologique. Ce dernier classe les objets ou systèmes de la manière suivante: deux objets appartiennent à la même classe topologique s'il est possible de déformer continument le premier objet en le second. Cette propriété globale rend le système robuste contre des perturbations locales telles que le désordre.
Les atomes froids constituent une plateforme idéale pour simuler les phases quantiques topologiques. Depuis l'invention du laser, les progrès en physique atomique et moléculaire ont permis un contrôle de la dynamique et des états internes des atomes. La réalisation de gaz quantiques,tels que les condensats de Bose-Einstein et les gaz dégénérés de Fermi, ainsi que la réalisation de réseaux optiques à l'aide de faisceaux lasers, permettent d'étudier ces nouvelles phases de la matière et de simuler aussi la physique du solide cristallin.
Dans cette thèse, nous nous concentrons sur l'etude d'isolants topologiques avec des atomes froids. Ces derniers sont isolants de volume mais possèdent des états de surface qui sont conducteurs, protégés par un invariant topologique. Nous traitons trois sujets principaux. Le premier sujet concerne la génération dynamique d'un isolant topologique de Mott. Ici, les interactions engendrent l'isolant topologique et ce, sans champ de jauge de fond. Le second sujet concerne la détection des isolants topologiques dans les expériences d'atomes froids. Nous proposons deux méthodes complémentaires pour caractériser celles-ci. Finalement, le troisième sujet aborde des thèmes au-delà de la définition standard d'isolant topologique. Nous avons d'une part proposé un algorithme efficace pour calculer la conductivité de Berry, la contribution topologique à la conductivité transverse lorsque l'énergie de Fermi se trouve dans une bande d'énergie. D'autre part, nous avons utilisé des méthodes pour caractériser les propriétés quantiques topologiques de systèmes non-périodiques.
L'étude des isolants topologiques dans les expériences d'atomes froids est un sujet de recherche récent et en pleine expansion. Dans ce contexte, cette thèse apporte plusieurs contributions théoriques pour la simulation de systèmes quantiques sur réseau avec des atomes froids.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Foell, III Charles Alden. "Luminescent properties of Pb-based (PbX) colloidal quantum dots (CQDs) in vacuum, on silicon and integrated with a silicon-on-insulator (SOI) photonic integrated circuit (PIC)." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57665.
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In the rapidly evolving field of experimental quantum information processing, one important sub-field pursues a potentially scalable implementation that transports quantum information encoded in photons throughout “photonic circuits” fabricated in a silicon wafer. A key component is an efficient on-demand source of these single photons, and this dissertation aimed to assess the feasibility of one proposed realization of such a source by integrating few PbSe colloidal quantum dots (CQDs, demonstrated single photon emitters in nanoparticle form) into the mode volume of an optical microcavity designed to efficiently direct quantum dot emission into a silicon photonic circuit. Although no direct evidence of {\it single} photon emission was observed, results prompted a number of follow-up experiments and considerable theoretical modeling to understand this quantum dot, photonic circuit system.
The methods of investigation included (1) temporally-, spectrally-, and spatially-resolved photoluminescence (PL) measurements of PbSe CQDs integrated into SOI PICs and relatable environments (solution, thick film, thin film), (2) temperature-dependent, air-exposure studies of PbSe CQD thick film PL, (3) development and application of kinetic and quantum mechanical cavity-coupled modeling that admit complete accounting of the photonic density of states, depolarization effects, and non-radiative decay, and (4) a photon coincidence test of single photon emission.
The main findings of this work are: (1) while capture of cavity-enhanced PbSe CQD emission into a silicon photonic circuit was demonstrated, the overall photon generate rate is inadequate for any useful implementation, (2) the measured coupling rate can be modeled and explained in terms of system parameters extracted from auxiliary experimental results obtained with the PbSe CQDs in isolation, or on isolated microcavities, and (3) consistent results could only be obtained after nontrivial depolarization factors and non-radiative decay processes are properly accounted for. From this it is clear that the performance of PbSe CQDs in this configuration of a single photon source in silicon is currently limited by a long-lived trap state with a several microsecond lifetime, and large depolarization effects that inhibit emission. Although plausible future efforts may mitigate these effects substantially, performance may still be hindered by the intrinsic emission strength of PbSe CQDs.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Ekanayake, Sobhath Ramesh Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "Qubit control-pulse circuits in SOS-CMOS technology for a Si:P quantum computer." Publisher:University of New South Wales. Electrical Engineering & Telecommunications, 2008. http://handle.unsw.edu.au/1959.4/43096.
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Microelectronics has shaped the world beyond what was thought possible at the time of its advent. One area of current research in this field is on the solid-state Si:P-based quantum computer (QC). In this machine, each qubit requires an individually addressed fast control-pulse for non-adiabatic drive and measure operations. Additionally, it is increasingly becoming important to be able to interface nanoelectronics with complementary metal-oxide-semiconductor (CMOS) technology. In this work, I have designed and demonstrated full-custom mixed-mode and full-digital fast control-pulse generators fabricated in a silicon-on-sapphire (SOS) CMOS commercial foundry process ?? a radio-frequency (RF) CMOS technology. These circuits are, fundamentally, fast monostable multivibrators. Initially, after the design specifications were decided upon, I characterized NFET and PFET devices and a n+-diffusion resistor from 500 nm and 250 nm commercial SOS-CMOS processes. Measuring their conductance curves at 300 300 K, 4.2 2 K, and sub-K (30 30 mK base to 1000 1000 mK) showed that they function with desirable behaviour although exhibiting some deviations from their 300 300 K characteristics. The mixed-mode first generation control-pulse generator was demonstrated showing that it produced dwell-time adjustable pulses with 100 100 ps rise-times at 300 K, 4.2 2 K, and sub-K with a power dissipation of 12 12 uW at 100 100 MHz. The full-digital second generation control-pulse generator was demonstrated showing accurately adjustable dwell-times settable via a control-word streamed synchronously to a shift-register. The design was based on a ripple-counter with provisions for internal or external clocking. This research has demonstrated that SOS-CMOS technology is highly feasible for the fabrication of control microelectronics for a Si:P-based QC. I have demonstrated full-custom SOS-CMOS mixed-mode and full-digital control circuits at 300 300 K, 4.2 2 K, and sub-K which suitable for qubit control.
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Duchon, Eric Nicholas. "Quantum Phase Transitions in the Bose Hubbard Model and in a Bose-Fermi Mixture." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386002245.
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FRANCESCHINI, PAOLO. "NOVEL SCHEMES FOR ULTRAFAST MANIPULATION OF QUANTUM MATERIALS." Doctoral thesis, Università Cattolica del Sacro Cuore, 2022. http://hdl.handle.net/10280/111822.
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La possibilità di controllare le proprietà elettroniche on-demand su una scala di tempo ultraveloce rappresenta una delle sfide più intriganti verso la realizzazione di dispositivi fotonici ed elettronici di nuova generazione. Stimolata da questo, negli ultimi decenni la ricerca scientifica ha concentrato la propria attenzione su diverse piattaforme a stato solido. Tra tutte, nanostrutture dielettriche (e metamateriali) e materiali correlati si presentano come i più promettenti candidati per la realizzazione di dispositivi dotati di nuove funzionalità. Al di là delle caratteristiche specifiche che rendono i dielettrici più adatti ad applicazioni in fotonica e i materiali correlati ai dispositivi elettronici, entrambe le categorie manifestano nuove funzionalità se soggetti ad uno stimolo esterno sotto forma di impulsi di luce con durata più breve della scala di tempo caratteristica del rilassamento dei gradi di libertà interni al sistema. Infatti, lo stato fuori equilibrio raggiunto a seguito di una foto-eccitazione presenta proprietà elettroniche ed ottiche di gran lunga differenti da quelle all'equilibrio. Pertanto, l'obiettivo di questo lavoro di tesi consiste nello sviluppo di nuovi metodi ed approcci sperimentali in grado di indurre, misurare e controllare nuove funzionalità in materiali complessi su una scala di tempo ultraveloce.The possibility to control the electronic properties on-demand on an ultrafast time scale represents one of the most exciting challenges towards the realization of new generation photonic and electronic devices. Triggered by this, in the last decades the research activity focused its attention to different solid-state platforms. Among all, dielectric nanostructures (and metamaterials) and correlated materials represent the most promising candidate for the implementation of devices endowed by new functionalities. Apart from the specific features making dielectrics more suitable for photonic applications and correlated materials for electronic devices, both categories exhibit new functionalities if subjected to an external stimulus in the form of excitation light pulses shorter than the relaxation timescale of the internal degrees of freedom of the system. Indeed, the out-of-equilibrium state achieved upon photoexcitation exhibits electronic and optical properties highly different from those at equilibrium. Therefore, the aim of this thesis work consists in the development of new methods and experimental approaches capable to induce, measure, and control new functionalities in complex materials on an ultrafast time scale.
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Wang, Fang. "Quantum phase transitions and fluctuations in space charge doped one unit-cell Bi2Sr2CaCu2O8+x." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS436.
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La transition supraconducteur-isolant en deux dimensions est une transition de phase quantique continue à la température du zéro absolu provoquée par des paramètres externes tels que le désordre, le champ magnétique ou la concentration de porteurs. De telles transitions ont été induites dans une variété de supraconducteurs bidimensionnels en ajustant différents paramètres externes et étudiées avec une analyse de renormalisation de taille finie. Il y a cependant assez peu d'uniformité dans les résultats car à la fois les systèmes supraconducteurs et les paramètres externes sont divers. Dans cette thèse, nous avons d'abord fabriqué des échantillons BSCCO-2212 d'épaisseur d'une cellule unité et de grande qualité avec la technique de collage anodique, une méthode originale d'exfoliation développée dans notre laboratoire pour préparer des cristaux 2D de haute qualité à partir de matériaux lamellaires massifs. Ensuite, nous avons provoqué la transition supraconducteur-isolant dans les échantillons fabriqués de Bi2.1Sr1.9CaCu2O8+x monocouche par dopage par charge d'espace, qui est une technique efficace de dopage électrostatique à effet de champ. Nous avons déterminé les paramètres critiques associés et développé un moyen fiable d'estimer le dopage dans la région non supraconductrice, un problème crucial et central dans ces matériaux. L'analyse par renormalisation de taille finie donne un dopage critique de 0,057 trous/Cu, une résistance critique de ~ 6.85 kOhm et un produit d'exposant critiques νz ~ 1,57. Ces résultats, ainsi que des travaux antérieurs sur d'autres matériaux, fournissent une image cohérente de la transition supraconducteur-isolant et de sa nature bosonique dans le régime sous-dopé de la supraconductivité émergente dans les supraconducteurs à haute température critique. Ensuite, dans la dernière partie de cette thèse, nous avons également étudié les effets de l'inhomogénéité et des fluctuations sur la transition supraconductrice à l'échelle mésoscopique et nanoscopique à la fois avec des simulations et des mesures de transport. L'utilisation d'un échantillon ultra-mince facilite également l'analyse sur deux fronts. Tout d'abord, en deux dimensions, les phénomènes de fluctuation liés à la transition supraconductrice sont exacerbés, facilitant l'analyse des changements de largeurs. Deuxièmement, les aspects liés à la percolation et au clustering peuvent être facilement simulés et comparés à des modèles analytiques. En particulier, les effets des fluctuations sur le côté surdopé et sous-dopé du diagramme de phase d'une monocouche de BSCCO-2212 sont discutés. Nous avons découvert que le régime de fluctuation dans la partie sous-dopée du diagramme de phase est fondamentalement différent de celui dans la partie où p > 0,19. Nous avons discuté du comportement possible des paires de Cooper liées à nos résultats expérimentaux, ainsi que d'une des théories pouvant l'expliquer (transition BEC-BCS)The superconductor-insulator transition in two dimensions is a continuous quantum phase transition at absolute zero temperature driven by external parameters like disorder, magnetic field, or carrier concentration. Such transitions have been induced in a variety of two dimensional superconductors by tuning different external parameters and studied with a finite-size scaling analysis. There is however not much uniformity in the findings as both the superconducting systems and the tuning parameters are diverse. In this thesis, we first fabricated high quality of one unit-cell BSCCO-2212 samples with anodic bonding technique, an original method of exfoliation developed in our laboratory for preparing high quality 2D crystals from layered bulk materials. Then we revealed the superconductor-insulator transition in the fabricated one unit-cell Bi2.1Sr1.9CaCu2O8+x by space charge doping, which in an effective field effect electrostatic doping technique. We determined the related critical parameters and develop a reliable way to estimate doping in the non-superconducting region, a crucial and central problem in these materials. Finite-size scaling analysis yields a critical doping of 0.057 holes/Cu, a critical resistance of ~ 6.85 kΩ and a scaling exponent product νz ~ 1.57. These results, together with earlier work in other materials, provide a coherent picture of the superconductor-insulator transition and its bosonic nature in the underdoped regime of emerging superconductivity in high critical temperature superconductors. Then in the latter part of this thesis, we also investigated the effects of inhomogeneity and fluctuations on superconducting transition on mesoscopic and nanoscopic scale both with simulation and with simulations and with analysis of transport measurements. The use of an ultra-thin sample also facilitates analysis on two fronts. Firstly, in two dimensions fluctuation phenomena related to the superconducting transition are exacerbated, making the analysis of changes in widths easier. Secondly aspects related to percolation and clustering can be easily simulated and compared with analytical models. Especially, the effects of fluctuations on the overdoped and underdoped side of the phase diagram of one unit-cell BSCCO-2212 are discussed. We discovered that the fluctuation regime in the underdoped part of the phase diagram is fundamentally different from that in the part where p > 0.19. We discussed the possible behaviour of cooper pairs related to our experimental results, as well as one existing theoretical explanation (BEC-BCStransition)
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Monniello, Leonard. "Excitation résonante de boîtes quantiques pour la génération d'états non-classiques de la lumière." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066052/document.
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Les développements en information quantique nécessitent le contrôle et la manipulation d'états quantiques. Parmi les systèmes en physique du solide, les boîtes quantiques semiconductrices sont de bons candidats pour réaliser des bits quantiques. La taille nanométrique de ces objets conduit à un confinement spatial à trois dimensions des porteurs : le spectre d'énergie est discret comme celui d'un atome. Ces objets sont étudiés pour leurs propriétés optiques, et notamment pour l'émission de photons uniques et indiscernables, qui sont des états quantiques de la lumière. Le travail de cette thèse consiste à étudier des boîtes quantiques uniques d'InAs/GaAs excitées à la résonance de leur transition optique, à l'aide d'impulsions lumineuses picosecondes. Grâce à une géométrie unidimensionnelle en guide d'onde, il est possible de s'affranchir de la lumière diffusée du laser d'excitation, et d'observer la luminescence résonante des boîtes. On atteint alors le régime d'oscillations de Rabi qui permet d'inscrire dans la boîte une superposition cohérente du système à deux niveaux, c'est un bit quantique. Cependant, le couplage entre la boîte et son environnement modifie les propriétés de cohérence des boîtes quantiques, limitant la possibilité de réaliser des opérations sur les qubits. Deux phénomènes principaux de décohérence ont été modélisés : l'interaction avec les phonons longitudinaux acoustiques de la matrice environnante de la boîte et le couplage avec le mode électromagnétique. Nous avons enfin étudié la statistique d'émission de photons des boîtes quantiques, et nous montrons qu'elles constituent de bonnes sources de photons uniques indiscernables, à la demandeDevelopments in quantum information require controlling and manipulating quantum bits. Among solid state emitters, semiconductor quantum dots seem promising to realize quantum bits. First, the nanometric size of those structures leads to the confinement of the carriers in the three directions of space, so that their energy spectrum becomes atom-like. Furthermore, they can easily be integrated into electronic and optic devices. Such structures are studied for their optical properties, especially the emission of single and indistinguishable photons, which are quantum states of light. In the present work InAs/GaAs quantum dots have been studied under resonant excitation with picosecond laser pulses. One-dimensional waveguiding geometry has been used to suppress the scattered excitation laser allowing the observation of a single dot resonant luminescence. The coupling between the laser and the dot leads to the Rabi oscillations regime which enables to address a coherent superposition of states in the two-level system, meaning a quantum bit. However, the coupling between the dot and its environment changes the coherence properties of the dots, limiting the time during which operations on the qubits are possible. Two main phenomena have been observed and studied: the interaction between the dots and the longitudinal acoustic phonons of the GaAs matrix and the coupling with the electromagnetic mode. Finally, the photon emission statistics of the quantum dots have been studied, showing that quantum dots are on demand good emitters of indistinguishable single photons
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Santos-Cottin, David. "Propriétés électroniques et de transport du semi-métal corrélé quasi-2D BaNiS2." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066139/document.
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Ce travail de thèse a pour but de clarifier le mécanisme de la transition métal-isolant (MIT) pilotée par le dopage électronique x du système quasi-2D BaCo1-xNixS2.Une optimisation de la croissance de monocristaux pour des taux de substitution allant de x = 0 à 1 a été nécessaire. Cela a permis de synthétiser de manière reproductible des monocristaux non lacunaires en soufre, de taille millimétrique et de haute qualité. L'analyse structurale de ces cristaux a permis d'établir une relation précise entre les distances métal-soufres et le taux de substitution x.Le travail de thèse a ensuite été focalisé sur l'étude des propriétés électroniques et de transport de BaNiS2 la phase métallique précurseur de la MIT. Les études de la structure électronique par photoémission résolue en angle (ARPES) et par des mesures d'oscillations quantiques ont révélées une surface de Fermi composée d'une poche d'électrons 2D centrée en Γ(Z) et d'une poche de trous positionnée à mi-distance suivant ΓM(ZA) quasi-2D avec une dispersion conique à kz =0. Une levée de dégénérescence des bandes à Γ et à X révèle la présence inattendue et importante d'un couplage spin-orbite et d'un couplage Rashba. Les mesures de magnétotransport ont pu être expliquées par un modèle qui implique que BaNiS2 est un semi-métal compensé avec trois voies de conduction. Des trous p1 et électrons e1 largement majoritaires et présentant des mobilités modérées ainsi que des trous p2 minoritaires de très haute mobilité.La cohérence de l'ensemble des mesures donne une image précise de la surface de Fermi de BaNiS2 et de ses propriétés électroniques plus bidimensionnelle que celle prévu par le calculs de bandes conventionnelleThis work aims to clarify the mechanism of the metal-insulator transition (MIT) driven by doping x in the quasi-2D BaCo1-xNixS2 system. First of all, synthesize of high quality single crystals with substitution level x varying in the full 0 - 1 range was fundamental. It appears that the mechanism of the metal-insulator transition is associated to a continuous modification of metal-sulfurs distances. Then, we focus on an investigated the electronic properties of BaNiS2, precursor metallic phase of the MIT. Studies of the electronic structure of BaNiS2 by angle-resolved photoemission spectroscopy (ARPES) and by quantum oscillation measurements reveal the existence of two pockets at the Fermi surface: an electron-like 2D pocket centered in Γ(Z) and a hole-like pocket quasi-2D at mi-distance along ΓM(ZA) with a conic-like dispersion in kz = 0 . Furthermore, data also show a very large spin-orbit splitting at Γ and Z which is unexpected in a 3d metal compound. From previous studies, we developed a model to explain magnetotransport properties of BaNiS2. This model involves that BaNiS2 is a three carriers compensated metal: a majority holes p1 and electrons e1 carriers with moderate mobilities and a minor holes p2 carriers with a high mobility. The two different holes carries observed in magneto-transport could be explain by an important variation of the hole-like pocket dispersion along kz. Measures realized during this thesis are consistent and allowed to know precisely the form of the Fermi surface of BaNiS2 and its electronic properties which are more bi-dimensional than predict by conventional calculation
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Pournia, Seyyedesadaf. "Exploring the Photoresponse and Optical Selection Rules in the Semiconductor Nanowires, Topological Quantum Materials and Ferromagnetic Semiconductor Nanoflakes using Polarized Photocurrent Spectroscopy." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627666632280473.
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Eriksson, Hjalmar. "From the quantum Hall effect to topological insulators : A theoretical overview of recent fundamental developments in condensed matter physics." Thesis, Uppsala University, Theoretical Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-126860.
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In this overview I describe the simplest models for the quantum Hall and quantum spin Hall effects, and give some general indications as to the description of topological insulators. As a background to the theoretical models I will first trace the development leading up to the description of topological insulators . Then I will present Laughlin's original model for the quantum Hall effect and briefly discuss its limitations. After that I will describe the Kane and Mele model for the quantum spin Hall effect in graphene and discuss its relation to a general quantum spin Hall system. I will conclude by giving a conceptual description of topological insulators and mention some potential applications of such states.
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Demion, Arnaud. "Transport électronique dans le graphène et les isolants topologiques 2D en présence de désordre magnétique." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4349.
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Dans cette thèse, nous étudions l’effet du désordre magnétique sur les propriétés de transport électronique du graphène et des isolants topologiques 2D de type HgTe. Le graphène et les isolants topologiques sont des matériaux dont les excitations électroniques sont assimilées à des fermions de Dirac sans masse. L’influence des impuretés magnétiques sur les propriétés de transport du graphène est étudiée dans le régime de forts champs électriques. En conséquence de la production de paires électron-trou, la réponse devient non linéaire et dépend de la polarisation magnétique. Nous étudions une transition entre un isolant topologique bi-dimensionnel conducteur, caractérisé par une conductance G = 2 (en quantum de conductance) et un isolant de Chern avec G = 1, induite par des impuretés magnétiques polariséesIn this thesis, we study the effect of a magnetic disorder on the electronic transport properties of graphene and HgTe-type 2D topological insulators. Graphene and topological insulators are materials whose electronic excitations are treated as massless Dirac fermions.The influence of magnetic impurities on the transport properties of graphene is investigated in the regime of strong applied electric fields. As a result of electron-hole pair creation, the response becomes nonlinear and dependent on the magnetic polarization.We investigate a transition between a two-dimensional topological insulator conduction state, characterized by a conductance G = 2 (in conductance quantum) and a Chern insulator with G = 1, induced by polarized magnetic impurities
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Thomas, Candice. "Strained HgTe/CdTe topological insulators, toward spintronic applications." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY090/document.
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Les isolants topologiques constituent une nouvelle classe de matériaux caractérisés par l'association d'un volume isolant et de surfaces conductrices. Avec des propriétés électroniques similaires au graphene, notamment un transport régit par des particules à énergie de dispersion linéaire couramment appelés fermions de Dirac ainsi qu'une protection topologique empêchant tout phénomène de rétrodiffusion, ces matériaux suscitent un intérêt grandissant dans la quête d'une électronique de faible consommation. En effet, la production de courants de spin non-dissipatifs et polarisés ainsi que la formation de courants de spin purs en l'absence de matériaux magnétiques constituent une partie des attentes de ces matériaux topologiques.L'objectif de cette thèse a été de démontrer expérimentalement le potentiel de l'isolant topologique HgTe pour des applications notamment dans le domaine de la l'électronique de spin ou spintronique.Pour ce faire, d'importants efforts ont été mis en œuvre pour améliorer le procédé de croissance par épitaxie par jets moléculaires.La composition chimique, la contrainte ainsi que la qualité des interfaces de la couche de HgTe ont été identifiées comme des axes majeurs de travail et d'optimisation afin d'obtenir une structure de bande inversée, l'ouverture d'un gap de volume, ainsi que pour protéger les propriétés électroniques des états de surface topologiques. Fort de ces caractéristiques, notre matériau possède à priori toutes les qualités nécessaires pour permettre de sonder les propriétés topologiques. Accéder à ces propriétés particulières est en particulier possible par des mesures d'effet Hall quantique sur des structures de type barres de Hall. La fabrication de ces dispositifs a néanmoins requis une attention particulière à cause de la forte volatilité du mercure et a nécessité le développement d'un procédé de nanofabrication à basses températures.Des mesures d'effet Hall quantique à très basses températures ont ensuite été réalisées dans un cryostat à dilution. Tout d'abord des couches épaisses de HgTe ont été mesurées et ont démontrées des mécanismes de transport très complexes mêlant les états de surface topologiques à d'autres contributions attribuées au volume et aux états de surface latéraux. La réduction de l'épaisseur des couches de HgTe a permis de limiter l'impact de ces contributions en les rendant négligeable pour les couches les plus fines. Dans ces conditions, ces structures ont affiché les propriétés attendues de l'effet Hall quantique avec notamment une annulation de la résistance. Avec ces propriétés, l'analyse en température de l'effet Hall quantique a permis de démontrer la nature des porteurs circulant sur les états de surface topologiques et de les identifier à des fermions de Dirac.Avec la mise en évidence de la nature topologique de notre système, l'étape suivante a été d'utiliser les propriétés topologiques et plus particulièrement le blocage entre le moment et le spin d'un électron pour tester le potentiel du système 3D HgTe/CdTe pour la spintronique. Premièrement, des mesures de pompage de spin ont été réalisées et ont mis en exergue la puissance de ces structures pour l'injection et la détection de spin. Deuxièmement, ces structures ont été implémentéessous la forme de jonction p-n dans l'idée de réaliser un premier dispositif de spintronique qui présente à ce jour des premiers signes de fonctionnementWith graphene-like transport properties governed by massless Dirac fermions and a topological protection preventing from backscattering phenomena, topological insulators, characterized by an insulating bulk and conducting surfaces, are of main interest to build low power consumption electronic building-blocks of primary importance for future electronics.Indeed, the absence of disorder, the generation of dissipation-less spin-polarized current or even the possibility to generate pure spin current without magnetic materials are some of the promises of these new materials.The objective of this PhD thesis has been to experimentally demonstrate the eligibility of HgTe three dimensional topological insulator system for applications and especially for spintronics.To do so, strong efforts have been dedicated to the improvement of the growth process by molecular beam epitaxy.Chemical composition, strain, defect density and sharpness of the HgTe interfaces have been identified as the major parameters of study and improvement to ensure HgTe inverted band structure, bulk gap opening and to emphasize the resulting topological surface state electronic properties. Verification of the topological nature of this system has then been performed using low temperature magneto-transport measurements of Hall bars designed with various HgTe thicknesses. It is worth noting that the high desorption rate of Hg has made the nanofabrication process more complex and required the development of a low temperature process adapted to this constraint. While the thicker samples have evidenced very complex transport signatures that need to be further investigated and understood, the thickness reduction has led to the suppression of any additional contributions, such as bulk or even side surfaces, and the demonstration of quantum Hall effect with vanishing resistance. Consequently, we have managed to demonstrate direct evidences of Dirac fermions by temperature dependent analysis of the quantum Hall effect. The next step has been to use the topological properties and especially the locking predicted between momentum and spin to test the HgTe potential for spintronics. Spin pumping experiments have demonstrated the power of these topological structures for spin injection and detection. Moreover, the implementation of HgTe into simple p-n junction has also been investigated to realize a first spin-based logic element