To see the other types of publications on this topic, follow the link: Semimetals.
Dissertations / Theses on the topic 'Semimetals'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Semimetals.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Trescher, Maximilian [Verfasser]. "Tilted Weyl Semimetals / Maximilian Trescher." Berlin : Freie Universität Berlin, 2018. http://d-nb.info/1176708244/34.
Full text
2
McCormick, Timothy M. "Electronic and Transport Properties of Weyl Semimetals." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu153204408441858.
Full text
3
Zhong, Shudan. "Linear and Nonlinear Electromagnetic Responses in Topological Semimetals." Thesis, University of California, Berkeley, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13421373.
Full textAbstract:
<p>The topological consequences of time reversal symmetry breaking in two dimensional electronic systems have been a focus of interest since the discovery of the quantum Hall effects. Similarly interesting phenomena arise from breaking inversion symmetry in three dimensional systems. For example, in Dirac and Weyl semimetals the inversion symmetry breaking allows for non-trivial topological states that contain symmetry-protected pairs of chiral gapless fermions. This thesis presents our work on the linear and nonlinear electromagnetic responses in topological semimetals using both a semiclassical Boltzmann equation approach and a full quantum mechanical approach. In the linear response, we find a ``gyrotropic magnetic effect" (GME) where the current density $j</p><p>B$ in a clean metal is induced by a slowly-varying magnetic field. It is shown that the experimental implications and microscopic origin of GME are both very different from the chiral magnetic effect (CME). We develop a systematic way to study general nonlinear electromagnetic responses in the low-frequency limit using a Floquet approach and we use it to study the circular photogalvanic effect (CPGE) and second-harmonic generation (SHG). Moreover, we derive a semiclassical formula for magnetoresistance in the weak field regime, which includes both the Berry curvature and the orbital magnetic moment. Our semiclassical result may explain the recent experimental observations on topological semimetals. In the end, we present our work on the Hall conductivity of insulators in a static inhomogeneous electric field and we discuss its relation to Hall viscosity.
4
Kim, Namshik. "Holographic gauge/gravity duality and symmetry breaking in semimetals." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/60622.
Full textAbstract:
We use the AdS/CFT correspondence (the holographic duality of gauge/gravity theory) to study exciton driven dynamical symmetry breaking in certain (2+1)-dimensional defect quantum field theories. These models can be argued to be analogs of the electrons with Coulomb interactions which occur
in Dirac semimetals and the results our study of these model systems are indicative of behaviours that might be expected in semimetal systems such as monolayer and double monolayer graphene. The field theory models have simple holographic duals, the D3-probe-D5 brane system and the D3-probe-D7 brane system. Analysis of those systems yields information about the strong coupling planar limits of the defect quantum field theories. We study the possible occurrence of exciton condensates in the strong coupling limit of single-defect theories as well as double monolayer theories where we find a rich and interesting phase diagram. The phenomena which we study include the magnetic catalysis of chiral symmetry breaking in monolayers and inter-layer exciton condensation in double monolayers. In the latter case, we find a solvable model where the current-current correlations functions in the planar strongly coupled field theory can be computed explicitly and exhibit interesting behavior. Although the models that we analyze differ in detail from real condensed matter systems, we identify some phenomena which can occur at strong coupling in a generic system and which could well be relevant to the ongoing experiments on multi-monolayer Dirac semimetals. An example is the spontaneous nesting of Fermi surfaces in double monolayers. In particular, we suggest an easy to observe experimental signature of this phenomenon.<br>Science, Faculty of<br>Physics and Astronomy, Department of<br>Graduate
5
Bennacer, Badis. "Acoustic plasmons and transverse modes in semimetals and semiconductors." Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280013.
Full text
6
Chu, Ruilin, and 储瑞林. "Numerical study of topological insulators and semi-metals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47163252.
Full textAbstract:
Topological insulators(TIs) constitute a novel state of quantum matter which possesses non-trivial topological properties. Although discovered only in the recent few years, TIs have attracted intensive interest among the community of condensed matter physics and material science. TIs are insulating in the bulk but have conductive gapless edge or surface states on the boundaries, which have their origin in the nontrivial bulk band topology that is induced by the strong spin-orbital interactions in the materials. Existing in all dimensions, TIs exhibit a variety of exotic physics such as quantum spin Hall effect, momentum-spin locked surface states, Dirac fermion transport, quantized anomalous Hall effect, Majorana fermions, etc. In this thesis,
I study the transport properties of 2D and 3D TIs by numerical approaches. As an introduction, a brief review of TIs is given. A detailed description of the numerical methods is also presented. The results can be summarized in four aspects. First, disorder is found be able to induce a non-trivial TI from an originally trivial band insulator, where the conductance of a two terminal device drops to nearly zero and then rises to form an anomalous plateau as disorder strength is increased, and finally all the states become localized. The real space Chern number calculation as well as the effective medium theory suggests that disorder is fundamentally responsible for the emerging of the extended helical edge states in this system. We also present a levitation and pair annihilation picture of the extended states for this model. Second, by making the 2D TIs into singly connected quantum point contacts(QPCs), I show a coherent and fast Aharonov-Bohm oscillation of conductance caused by the quantum interference of the helical edge states. This oscillation not only happens against weak magnetic field but also against the gate voltage in the zero-field condition.
This results in a giant edge magnetoresistance of the device in weak magnetic fields. The amplitude of the magnetoresistance is controllable by adjusting either the
QPCs' slit width or the interference loop size in the device. The oscillation is found robust against disorder. Third, by applying a uniform spin-splitting Zeeman field in the bulk of the 3D TI whose surface states can be viewed as massless Dirac fermions,
I find chiral edge states on the gapped surfaces of the 3D TI, which can be considered as interface states between domains of massive and massless Dirac fermions.
Effectively these states are result of splitting of a perfect interface conducting channel. This picture is confirmed by the Landauer-B?ttiker calculations in four-terminal Hall bars. Finally, I propose the concept of topological semi-metals. By calculating the local density of states on the surfaces, I demonstrate that surface states and the gapless
Dirac cone already exist in the system although the bulk is not gapped. We show how the uni-axial strain induces an insulating band gap and turn the semi-metal into true TI. We predict existence of quantum spin Hall effect in the thin films made of these materials, which can be significantly enhanced by disorders.<br>published_or_final_version<br>Physics<br>Doctoral<br>Doctor of Philosophy
7
Mao, Ting, and 毛汀. "Theoretical studies of topological DIII-class chains and Weyl semimetals / y Ting Mao, MSci. Nanjing University." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2015. http://hdl.handle.net/10722/212613.
Full textAbstract:
Topological insulators and superconductors, which are featured by not only the topological characteristics of their gapped bulk band structure but also the special edge or surface states, have attracted great attention in the past few years. A complete classification of topological insulators and superconductors in terms of symmetry and spatial dimension has been established, while the application of their surface states remains a challenge. The gapless phases which have topologically stable Fermi surfaces could also exhibit peculiar surface states and topological transport phenomena in the bulk. In this thesis, the topological DIII-classs superconducting chains and the application of its Majorana edge states are studied. On the other hand, Weyl semimetals, as the representative example of topological gapless phases, and its exotic transport phenomena are also investigated.
Majorana edge states have been a focus of condensed matter research for their potential applications in topological quantum computation, which appear in the topological DIII-class superconducting chains protected by both the particle-hole and time reversal symmetries. We utilize two charge-qubit arrays to explicitly simulate one type of DIII-class superconducting chains and the universal quantum operations performed on the Majorana edge states. It is shown that combined with one braiding operation, universal single-qubit operations on a Majorana-based qubit can be implemented by a controllable inductive coupling between two charge qubits at the ends of the arrays. It is further shown that in a similar way, a controlled-NOT gate for two topological qubits can be simulated in four charge-qubit arrays. Although the current scheme may not truly realize topological quantum operations, we elaborate that the operations in charge-qubit arrays are indeed robust against certain local perturbations.
Weyl semimetals possess nontrivial Fermi surface topology in that the pair of Weyl points with opposite topological charges is separated from each other in momentum space. The physical manifestations of this Fermi surface topology are protected surface states and exotic transport phenomena including the anomalous Hall effect as well as the chiral magnetic effect. By studying the path integral measure under the chiral transformation, it is shown that these transport phenomena can be described by the chiral anomaly which appears when the chiral Weyl fermion couples to the topologically nontrivial gauge field. The case of the gauge anomaly for the Weyl fermion coupled to a non-Abelian gauge field is also discussed.<br>published_or_final_version<br>Physics<br>Doctoral<br>Doctor of Philosophy
8
Villanova, John William. "Examining Topological Insulators and Topological Semimetals Using First Principles Calculations." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82959.
Full textAbstract:
The importance and promise that topological materials hold has been recently underscored by the award of the Nobel Prize in Physics in 2016 ``for theoretical discoveries of topological phase transitions and topological phases of matter." This dissertation explores the novel qualities and useful topologically protected surface states of topological insulators and semimetals.
Topological materials have protected qualities which are not removed by weak perturbations. The manifestations of these qualities in topological insulators are spin-momentum-locked surface states, and in Weyl and Dirac semimetals they are unconventional open surface states (Fermi arcs) with anomalous electrical transport properties. There is great promise in utilizing the topologically protected surface states in electronics of the future, including spintronics, quantum computers, and highly sensitive devices. Physicists and chemists are also interested in the fundamental physics and exotic fermions exhibited in topological materials and in heterostructures including them.
Chapter 1 provides an introduction to the concepts and methods of topological band theory. Chapter 2 investigates the spin and spin-orbital texture and electronic structures of the surface states at side surfaces of a topological insulator, Bi2Se3, by using slab models within density functional theory. Two representative, experimentally achieved surfaces are examined, and it is shown that careful consideration of the crystal symmetry is necessary to understand the physics of the surface state Dirac cones at these surfaces. This advances the existing literature by properly taking into account surface relaxation and symmetry beyond what is contained in effective bulk model Hamiltonians.
Chapter 3 examines the Fermi arcs of a topological Dirac semimetal (DSM) in the presence of asymmetric charge transfer, of the kind which would be present in heterostructures. Asymmetric charge transfer allows one to accurately identify the projections of Dirac nodes despite the existence of a band gap and to engineer the properties of the Fermi arcs, including spin texture. Chapter 4 investigates the effect of an external magnetic field applied to a DSM. The breaking of time reversal symmetry splits the Dirac nodes into topologically charged Weyl nodes which exhibit Fermi arcs as well as conventionally-closed surface states as one varies the chemical potential.<br>Ph. D.
9
Sbierski, Björn [Verfasser]. "On disorder effects in topological insulators and semimetals / Björn Sbierski." Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1102197114/34.
Full text
10
Lau, Alexander. "Symmetry-enriched topological states of matter in insulators and semimetals." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-233930.
Full textAbstract:
Topological states of matter are a novel family of phases that elude the conventional Landau paradigm of phase transitions. Topological phases are characterized by global topological invariants which are typically reflected in the quantization of physical observables. Moreover, their characteristic bulk-boundary correspondence often gives rise to robust surface modes with exceptional features, such as dissipationless charge transport or non-Abelian statistics. In this way, the study of topological states of matter not only broadens our knowledge of matter but could potentially lead to a whole new range of technologies and applications. In this light, it is of great interest to find novel topological phases and to study their unique properties.
In this work, novel manifestations of topological states of matter are studied as they arise when materials are subject to additional symmetries. It is demonstrated how symmetries can profoundly enrich the topology of a system. More specifically, it is shown how symmetries lead to additional nontrivial states in systems which are already topological, drive trivial systems into a topological phase, lead to the quantization of formerly non-quantized observables, and give rise to novel manifestations of topological surface states. In doing so, this work concentrates on weakly interacting systems that can theoretically be described in a single-particle picture. In particular, insulating and semi-metallic topological phases in one, two, and three dimensions are investigated theoretically using single-particle techniques.
11
Ekahana, Sandy Adhitia. "Investigation of topological nodal semimetals through angle-resolved photoemission spectroscopy." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:afed6156-7aa2-4ba9-afd1-af53d775494f.
Full textAbstract:
Nodal semimetals host either degenerate points (Dirac/Weyl points) or lines whose band topology in Brillouin zone can be classified either as trivial (normal nodal semimetals) or non trivial (topological nodal semimetals). This thesis investigates the electronic structure of two different categories of topological nodal semimetals probed by angleresolved photoemission spectroscopy (ARPES): The first material is Indium Bismuth (InBi). InBi is a semimetal with simple tetragonal structure with P4/nmm space group. This space group is predicted to host protected nodal lines along the perpendicular momentum direction at the high symmetry lines of the Brillouin zone boundary even under strong spin-orbit coupling (SOC) situation. As a semimetal with two heavy elements, InBi is a suitable candidate to test the prediction. The investigation by ARPES demonstrates not only that InBi hosts the nodal line in the presence of strong SOC, it also shows the signature of type-II Dirac crossing along the perpendicular momentum direction from the center of Brillouin zone. However, as the nodal line observed is trivial in nature, there is no exotic drumhead surface states observed in this material. This finding demonstrates that Dirac crossings can be protected in a non-symmorphic space group. The second material is NbIrTe<sub>4</sub> which is a semimetal that breaks inversion symmetry predicted to host only four Weyl points. This simplest configuration is confirmed by the measurement from the top and bottom surface of NbIrTe<sub>4</sub> showing only a pair of Fermi arcs each. Furthermore, it is found that the Fermi arc connectivity on the bottom surface experiences re-wiring as it evolves from Weyl points energy to the ARPES Fermi energy level. This change is attributed to the hybridisation between the surface and the bulk states as their projection lie within the vicinity of each other. The finding in this work demonstrates that although Fermi arcs are guaranteed in Weyl semimetals, their shape and connectivity are not protected and may be altered accordingly.
12
Du, Xu. "Magnetotransport and tunneling study of the semimetals bismuth and graphite." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008357.
Full text
13
Oumous, Hassan. "Fabrication and characterisation of CuInSeâ†2 films on large subtrates for solar cell devices." Thesis, University of Newcastle Upon Tyne, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329544.
Full text
14
Lee, Kiyoung. "Spin dependent transport in semiconductor and semimetal materials." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610139.
Full text
15
Osterhoudt, Gavin Barnes. "Spectroscopy of Topological Materials:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:109002.
Full textAbstract:
Thesis advisor: Kenneth S. Burch<br>Since their first experimental realizations in the 2000s, bulk electronic topological materials have been one of the most actively studied areas of condensed matter physics. Among the more recently discovered classes of topological materials are the Weyl semimetals whose low energy excitations behave like massless, relativistic particles with well-defined chirality. These material systems display exotic behavior such as surface Fermi arc states, and the chiral anomaly in which parallel magnetic and electric fields lead to an imbalance of left- and right-handed particles. Much of the research into these materials has focused on the electronic properties, but relatively little has been directed towards understanding the vibrational properties of these systems, or of the interplay between the electronic and vibrational degrees of freedom. Further, the technological potential of these materials is still underdeveloped, with the search for physical properties enhanced by the topological nature of these materials being sought after. In this dissertation we address both of these issues. In Chapters III and IV we present temperature dependent Raman investigations of the the Weyl semimetals WP2, NbAs, and TaAs. Measurements of the optical phonon linewidths are used to identify the available phonon decay paths, with ab-initio calculations and group theory used to aid the interpretation of these results. We find that some phonons display linewidths indicative of dominant decay into electron-hole pairs near the Fermi surface, rather than decay into acoustic phonons. In light of these results we discuss the role of phonon-electron coupling in the transport properties of these Weyl semimetals. In Chapter V, we discuss the construction of our "PVIC" setup for the measurement of nonlinear photocurrents. We discuss the experimental capabilities that the system was designed to possess, the operating principles behind key components of the system, and give examples of the operating procedures for using the setup. The penultimate chapter, Chapter VI, presents the results of photocurrent measurements using this setup on the Weyl semimetal TaAs. Through careful analysis of the photocurrent polarization dependence, we identify a colossal bulk photovoltaic effect in this material which exceeds the response displayed by previously studied materials by an order of magnitude. Calculations of the second-order optical conductivity tensor show that this result is consistent with the divergent Berry connection of the Weyl nodes in TaAs. In addition to these topics, Chapter II addresses the results of Raman measurements on thin film heterostructures of the topological insulator Bi2Se3 and the magnetic semiconductor EuS. By investigating the paramagnetic Raman signal in films with different compositions of EuS and Bi2Se3 we provide indirect evidence of charge transfer between the two layers. We also track the evolution of phonon energies with varying film thicknesses on multiple substrates which provides insight into the interfacial strain between layers. We conclude the dissertation in Chapter VII with a summary of the main results from each preceding chapter, and give suggestions for future experiments that further investigate these topics<br>Thesis (PhD) — Boston College, 2020<br>Submitted to: Boston College. Graduate School of Arts and Sciences<br>Discipline: Physics
16
Hirschberger, Maximilian Anton. "Quasiparticle Excitations with Berry Curvature in Insulating Magnets and Weyl Semimetals." Thesis, Princeton University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10286472.
Full textAbstract:
<p> The concept of the geometric Berry phase of the quantum mechanical wave function has led to a better theoretical understanding of natural phenomena in all fields of fundamental physics research. In condensed matter physics, the impact of this theoretical discovery has been particularly profound: The quantum Hall effect, the anomalous Hall effect, the quantum spin Hall effect, magnetic skyrmions, topological insulators, and topological semimetals are but a few subfields that have witnessed rapid developments over the three decades since Michael Berry's landmark paper. In this thesis, I will present and discuss the results of three experiments where Berry's phase leads to qualitatively new transport behavior of electrons or magnetic spin excitations in solids.</p><p> We introduce the theoretical framework that leads to the prediction of a thermal Hall effect of magnons in Cu(1,3-bdc), a simple two-dimensional layered ferromagnet on a Kagomé net of spin <i>S</i> = 1/2 copper atoms. Combining our experimental results measured down to very low temperatures <i>T</i> = 0.3 K with published data from inelastic neutron scattering, we report a quantitative comparison with the theory. This confirms the expected net Berry curvature of the magnon band dispersion in this material.</p><p> Secondly, we have studied the thermal Hall effect in the frustrated pyrochlore magnet Tb<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>, where the thermal Hall effect is large in the absence of long-range magnetic order. We establish the magnetic nature of the thermal Hall effect in Tb<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>, introducing this material as the first example of a paramagnet with non-trivial low-lying spin excitations. Comparing our results to other materials with zero thermal Hall effect such as the classical spin ice Dy<sub>2</sub>Ti<sub> 2</sub>O<sub>7</sub> and the non-magnetic analogue Y<sub>2</sub>Ti<sub>2</sub>O<sub> 7</sub>, we carefully discuss the experimental limitations of our setup and rule out spurious background signals.</p><p> The third and final chapter of this thesis is dedicated to electrical transport and thermopower experiments on the half-Heusler material GdPtBi. A careful doping study of the negative longitudinal magnetoresistance (LMR) establishes GdPtBi as a new material platform to study the physical properties of a simple Weyl metal with only two Weyl points (for magnetic field along the crystallographic ⟨111⟩ direction). The negative LMR is associated with the theory of the chiral anomaly in solids, and a direct consequence of the nonzero Berry curvature of the energy band structure of a Weyl semimetal. We compare our results to detailed calculations of the electronic band structure. Moving beyond the negative LMR, we report for the first time the effect of the chiral anomaly on the longitudinal thermopower in a Weyl semimetal.</p><p>
17
de, Coster George. "Effective Soft-Mode Theory of Strongly Interacting Fermions in Dirac Semimetals." Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24235.
Full textAbstract:
We present an effective field theory for interacting electrons in clean semimetals (both three dimensional Dirac semimetals and graphene) in terms of their soft or massless bosonic degrees of freedom. We show, by means of a Ward identity, that the intrinsic semimetal ground state breaks the Sp(4M) symmetry of the theory. In Fermi liquids this enables one to identify the massive, non-Goldstone modes of the theory and integrate them out. Due to the vanishing density of states in semimetals, unlike in Fermi liquids, both Goldstone and non-Goldstone modes are equally soft, and so all two-particle correlations need to be kept. The resulting theory is not perturbative with respect to the electron-electron interaction; rather, it is controlled by means of a systematic loop expansion and allows one to determine the exact asymptotic form of observables in the limits of small frequencies and/or wave vectors. Equivalently, it provides a mechanism of determining the long time-tail and long wavelength behavior of observables and excitations. As a representative application, we use the theory to compute the zero-bias anomaly for the density of states for both short and long-range interactions in two and three dimensions. We find that the leading nonanalyticity in semimetals with a long-ranged interaction appears at the same order in frequency as the one in Fermi liquids, since the effects of the vanishing density of states at the Fermi level are offset by the breakdown of screening. Consequently, we are able to provide a logical scheme to determine the leading non-analytical behavior of observables in semimetals using knowledge of the corresponding non-analyticities in a Fermi liquid.<br>2020-01-11
18
Haubold, Erik [Verfasser], Bernd [Gutachter] Büchner, and Oliver [Gutachter] Rader. "Electronic structure of topological semimetals / Erik Haubold ; Gutachter: Bernd Büchner, Oliver Rader." Dresden : Technische Universität Dresden, 2019. http://d-nb.info/1226944779/34.
Full text
19
Nilforoushan, Niloufar. "Out-of-equilibrium electron dynamics of Dirac semimetals and strongly correlated materials." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS573/document.
Full textAbstract:
Les matériaux quantiques ont récemment introduit en physique de la matière condensée pour unifier tous les matériaux dans lesquels les fortes corrélations électroniques gouvernent les propriétés physiques du système (e.g. les isolants de Mott) et les matériaux dont les propriétés électroniques sont déterminées par la géométrie de la fonction d’onde (e.g. matériaux de Dirac). Ces matériaux montrent des propriétés émergentes résultantes de l’intrication de différents degrés de libertés : la charge, le spin et le moment orbital, donnant lieu aux propriétés topologiques des électrons. L’étude de ces interactions et des compétitions entre les degrés de liberté pertinents nécessite l’utilisation de techniques pompe-sonde ultra-rapides. Particulièrement, les pulses laser femtosecondes interagissent uniquement avec les électrons pour les placer dans un état hors-équilibre décrit par des distributions de type non Fermi-Dirac. La dynamique subséquente implique de nombreux processus, avec un temps de relaxation relié aux constantes de couplage. De plus, dans les techniques résolues en temps, la lumière peut agir comme un paramètre externe, différent des paramètres thermodynamiques, pour explorer le diagramme de phase. Cela nous donne l’opportunité de stabiliser de nouveaux états inaccessibles par des chemins thermiques quasi-adiabatiques ou de manipuler les propriétés physiques des systèmes.Dans cette thèse, nous avons réalisé différentes expériences dans le but d’étudier les propriétés à l’équilibre et hors équilibre de deux matériaux corrélés: BaCo₁₋ₓNiₓS₂ et (V₁₋ₓMₓ)₂O₃.La première partie de ce projet a été dédiée principalement à l’étude de BaNiS₂, le précurseur métallique de la transition de Mott dans BaCo₁₋ₓNiₓS₂ . En utilisant l’ARPES, nous avons étudié la structure de bandes électroniques de BaNiS₂ dans toute la zone de Brillouin. L’expérience, combinée avec des calculs théoriques, révèle un nouveau type de cône de Dirac bidimensionel à caractère orbitalaire d et induit par les corrélations. Le croisement des bandes est protégé par les symétries particulières de la structure cristalline. Nous avons aussi mesuré la structure de bandes de l’isolant de Mott BaCoS₂ dans ses phases magnétique et non magnétiques.Dans la seconde partie, nous avons étudié la dynamique électronique hors équilibre de BaNiS₂ et (V₁₋ₓMx)₂O₃. Grâce à des mesures tr-ARPES et tr-Réflectivité, nous avons observé une renormalisation non thermique et ultra-rapide du cône de Dirac dans BaNiS₂. Ce phénomène est purement provoqué par les excitations électroniques et est stabilisé par l’intéraction entre les électrons et les phonons. De plus, en utilisant différentes techniques pompe-sonde (tr-XRD basé sur XFEL et tr-Réflectivité) nous avons aussi exploré des phases hors-équilibre du matériau prototype de Mott-Hubbard (V₁₋ₓMx)₂O₃ appartenant à différentes parties de son diagramme de phase. Nos résultats montrent une phase transitoire non thermique se développant immédiatement après la photoexcitation ultra-rapide et durant quelques picosecondes dans les phases métallique et isolantes. Cette phase transitoire est accompagné par une distorsion structural qui correspond à un durcissement du réseau et est marqué par un “blue shift” du mode phononique A₁g. Nos résultats soulignent l’importance du remplissage des orbitales aussi bien que des effets important des forts couplages électron-réseau sélectifs dans les matériaux fortement corrélés<br>Quantum materials is a new term in condensed matter physics that unifies all materials in which strong electronic correlation governs physical properties of the system (e.g. Mott insulators) and materials whose electronic properties are determined by the geometry of the electronic wave function (e.g. Dirac materials). These materials show emergent properties– that is, properties that only appear by intricate interactions among many degrees of freedom, such as charge, spin and orbital, giving rise to topological properties of electrons. The study of these interactions and competitions between the relevant degrees of freedom demands applying ultrafast pump-probe techniques. Particularly, femtosecond laser pulses act only on the electrons and set them to an out-of-equilibrium state inexplicable by the Fermi-Dirac distribution. The ensuing dynamics involves various processes and the rate at which the relaxation occurs is related to the coupling constants. Moreover, in time-resolved pump-probe techniques light can act as an additional external parameter to change of the phase diagram – different from thermodynamic parameters. It gives us the opportunity of stabilizing new states inaccessible by quasi-adiabatic thermal pathways or eventually manipulating the physical properties of the systems.In this thesis, we performed different experiments in order to study the equilibrium and out-of-equilibrium properties of two correlated compounds: BaCo₁₋ₓNiₓS₂ and (V₁₋ₓMₓ)₂O₃.The first part of the project was mainly devoted to the study of BaNiS₂ that is the metallic precursor of the Mott transition in BaCo₁₋ₓNiₓS₂. By applying ARPES, we studied the electronic band structure of BaNiS₂ in its entire Brillouin zone. These results combined with some theoretical calculations give evidence of a novel correlation-induced and two-dimensional Dirac cone with d-orbital character. The band crossing is protected by the specific symmetries of the crystal structure. We also investigated the electronic band structure of the Mott insulator BaCoS₂ in its magnetic and nonmagnetic phases.In the second part, we studied the out-of-equilibrium electron dynamics of BaNiS₂ and (V₁₋ₓMx)₂O₃. By means of tr-ARPES and tr-reflectivity measurements, we observed an ultrafast and non-thermal renormalization of the Dirac cone in BaNiS₂ . This phenomenon is purely provoked by the electronic excitation and is stabilized by the interplay between the electrons and phonons. Moreover, by applying various pump-probe techniques (XFEL-based tr-XRD and tr-Reflectivity) we also explored the out-of-equilibrium phases of the prototype Mott-Hubbard material (V₁₋ₓMx)₂O₃ in different parts of its phase diagram. Our results show a transient non-thermal phase developing immediately after ultrafast photoexcitation and lasting few picoseconds in both metallic and insulating phases. This transient phase is followed by a structural distortion that corresponds to a lattice hardening and is marked by a “blue shift” of the A₁g phonon mode. These results underline the importance of the orbital filling as well as the strong effect of the selective electron-lattice coupling in the strongly correlated materials
20
Khalaf, Eslam [Verfasser], and Walter [Akademischer Betreuer] Metzner. "Mesoscopic phenomena in topological insulators, superconductors and semimetals / Eslam Khalaf ; Betreuer: Walter Metzner." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1137510145/34.
Full text
21
Schilling, Micha Benjamin [Verfasser], and Martin [Akademischer Betreuer] Dressel. "Optical studies on Dirac and Weyl semimetals / Micha Benjamin Schilling ; Betreuer: Martin Dressel." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2018. http://d-nb.info/1173163816/34.
Full text
22
Vidal, Jordina. "Modelling for transient optically induced metal-insulator transitions in narrow-gap semiconductors and semimetals." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/17361.
Full text
23
Cheng, Tak Keung. "The excitation andn dynamics of coherent lattice vibrations in semimetals and narrow-gap semiconductors." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12008.
Full text
24
Guggenheim, Charles Moses [Verfasser], Martin [Gutachter] Zirnbauer, and Alexander [Gutachter] Altland. "Weyl semimetals: Euler structures and disorder / Charles Moses Guggenheim ; Gutachter: Martin Zirnbauer, Alexander Altland." Köln : Universitäts- und Stadtbibliothek Köln, 2020. http://d-nb.info/1219652415/34.
Full text
25
Rancati, Andrea. "Ab initio simulations of topological phase transitions in Dirac semimetal Cd3As2 doped with Zn and Mn impurities." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-80767.
Full textAbstract:
In this work we exploit the unique characteristics of a Dirac semimetal material to be symmetry-protected, to investigate dierent topological phase transitions provided by chemical dopings, focusing in particular on the electronic, magnetic and topological properties of the doped systems, studied by the mean of rst-principles methods based on density functional theory (DFT) approach. In particular these doped systems, besides being of interest for investigating the role of topology in solid state physics, could have a great potential for practical application since the dierent topological phases that come along with the chemical dopings allow one to exploit the unique properties of topological materials. The starting point for our study will be the material called cadmium-arsenide (Cd3As2), an example of a topological Dirac semimetal, which is chemically stable at ambient conditions. Chapter I presents a general introduction to topology, especially in condensed matter physics, and to the main physical properties of the topological materials we mentioned. Then, in chapter II, we briey present the methods and the computational tools that we used for our study. In chapter III a more detailed introduction to our work is given, along with a schemetic view of the path we followed, together with the results that we obtained for pristine Cd3As2, which we use as bench mark for our computational methods. Finally, in chapter IV and V, the results for the doped systems are presented and discussed, respectevely for the non-magnetic (IV) and magnetic (V) dopings. Our study has enabled us to discern how doping can give rise to see dierent topological phase transitions. Specically our work shows that dierent realizations of non-magnetic doping gives rise to dierent topological phases: the topological Weyl semimetal phase, which is of great interest since it can support a robust quantum spin Hall eect, and a very special mixed Dirac + Weyl phase, where surprisingly both a Dirac and a Weyl phase can coexist in the same system. Furthermore, magnetically doped systems show the emergence of a magnetic Weyl phase, which can support a quantum anomalous Hall eect. Our work can be the starting point for future studies, both theoretical and experimental, in which the unique physical properties we found in the doped Cd3As2 systems can be further investigated, in order to exploit them for practical applications.
26
Topp, Andreas [Verfasser], and Christian R. [Akademischer Betreuer] Ast. "Probing the electronic structure of new 3D Dirac semimetals / Andreas Topp ; Betreuer: Christian R. Ast." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1193492076/34.
Full text
27
Neubauer, David [Verfasser], and Martin [Akademischer Betreuer] Dressel. "Optical and magneto-optical investigations on 3D Dirac- and Weyl-semimetals / David Neubauer ; Betreuer: Martin Dressel." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1136319506/34.
Full text
28
Naumann, Marcel [Verfasser], Elena [Akademischer Betreuer] Hassinger, Elena [Gutachter] Hassinger, and Clemens [Gutachter] Laubschat. "The longitudinal magnetoresistance of Weyl semimetals / Marcel Naumann ; Gutachter: Elena Hassinger, Clemens Laubschat ; Betreuer: Elena Hassinger." München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1190818817/34.
Full text
29
Yang, Hung-Yu. "Novel Electromagnetic Responses in Topological Semimetals: Case Studies of Rare-Earth Monopnictides and RAlX Material Family." Thesis, Boston College, 2021. http://hdl.handle.net/2345/bc-ir:109188.
Full textAbstract:
Thesis advisor: Fazel Tafti<br>Since the idea of topology was realized in real materials, the hunt is on for new candidates of topological semimetals with novel electromagnetic responses. For example, topological states can be highly conductive due to a topological protection, which can be destroyed in a magnetic field and lead to an extremely high magnetoresistance. In Weyl semimetals, a transverse current that would usually require a magnetic field to emerge, can be generated by intrinsic Berry curvature without a magnetic field -- the celebrated anomalous Hall effect. In this dissertation, both phenomena mentioned above are studied in rare-earth monopnictides and RAlX material family (R=rare-earths, X=Ge/Si), respectively. The monopnictides are ideal for the study of extreme magnetoresistance because of their topological transitions and abundant magnetic phases. In LaAs, we untied the connection between topological states and the extreme magnetoresistance, the origin of which is clarified. In HoBi, we found an unusual onset of extreme magnetoresistance controlled by a magnetic phase dome. On the other hand, RAlX material family is a new class of Weyl semimetals breaking both inversion and time-reversal symmetries. In particular, in PrAlGeₓSi₁₋ₓ (x=0-1), we unveiled the first transition from intrinsic to extrinsic anomalous Hall effect in ferromagnetic Weyl semimetals, and the role of topology is discussed. In CeAlSi, we found that the Fermi level can be tuned as close as 1 meV away from the Weyl nodes; moreover, a novel anomalous Hall response appears only when the Fermi level is tuned to be near the Weyl nodes. Thus, we established a new transport response solely induced by Weyl nodes<br>Thesis (PhD) — Boston College, 2021<br>Submitted to: Boston College. Graduate School of Arts and Sciences<br>Discipline: Physics
30
Theóphilo, Carolina Yume Sawamura. "Análise de elementos potencialmente tóxicos em material biológico da Ilha da Trindade, Brasil." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/21/21137/tde-26112014-161310/.
Full textAbstract:
A Ilha da Trindade está localizada a aproximadamente 1150 km da costa de Vitória-ES, é uma das ilhas oceânicas brasileiras e está sob o domínio da Marinha do Brasil. Desde o início de sua ocupação sofreu algumas influências antrópicas, como a derrubada de árvores e a introdução de animais (porcos e cabras). Os metais oriundos da costa ou de navios que passam pela região, estão em destaque entre os contaminantes ambientais que podem alterar o ecossistema da ilha. Dessa forma, o objetivo desse trabalho foi quantificar Al, As, Cd, Cu, Fe, Mn, Ni, Pb, Se, Zn e Hg em 300 amostras, compostas por músculo de duas espécies de caranguejo e de fígado e músculo de peixes (duas espécies) e aves (três espécies). Foram verificadas se existiam relações entre parâmetros biológicos (sexo, comprimento, peso), diferenças entre tecidos e entre os períodos de coleta. Nos caranguejos a concentração de Fe em G. lagostoma, e Zn em G. grapsus, foram maiores nos meses mais quentes, nos quais a atividade biológica é maior, sendo uma possível causa para maiores concentrações. Diferentemente dos caranguejos, a espécie M. niger (peixe) apresentou maiores concentrações (Al no músculo e Fe e Zn no Fígado) nos meses mais frios, as concentrações em peixes envolvem muitos fatores além da sazonalidade. Para ambas as espécies de peixes as concentrações de Fe e Zn foram maiores no fígado, assim como para P. arminjoniana (ave) as concentrações de Cu, Fe e Zn também foram maiores no fígado, como era esperado, pois, o fígado é um tecido com grande capacidade de acumular poluentes. Alguns elementos apresentaram correlações com o peso e/ou comprimento, porém todas muito baixas, com exceção do Zn em G. grapsus. Todas as análises de Hg realizada ficaram abaixo do limite de quantificação do método (17,7 µg kg-1). Os metais e semimetais apresentaram resultados semelhantes a estudos desenvolvidos em outras regiões.<br>The Trindade Island is located approximately 1150 km from the coast of Vitória-ES, is one of Brazilian oceanic islands and is under the control of the Brazilian Navy. At the time the occupation began the island suffered some anthropogenic influences, such as the removal of trees and the animals introduction (pigs and goats). Metals originating from the shore or from ships passing through the region, are highlighting among the environmental contaminants that can change the ecosystem of the island. So the aim of this study was to quantify Al, As, Cd, Cu, Fe, Mn, Ni, Pb, Se, Zn and Hg in three hundred samples of muscle of two species of crab and liver and muscle of fish (two species) and seabirds (three species). The relationships between biological parameters (sex, length, weight), differences between tissues and between sampling periods were checked. The concentration of Fe, G. lagostoma (crab), and the Zn, in G. grapsus (crab), showed higher concentrations in the warmer months, in which biological activity is greater, being a possible cause for higher concentrations. Different from crabs, the species M. niger (fish) presented higher concentrations (Al in the muscle and Fe and Zn in the liver) in the colder months, concentrations in fish involve many factors besides the seasonality. For both species of fish concentrations of Fe and Zn were higher in the liver as well as for P. arminjoniana (seabird) concentrations of Cu, Fe and Zn were higher in the liver, like was expected, because the liver is a tissue with a great capacity to accumulate pollutants. Some elements showed correlations with the weight and/or length, but all very low, with the exception of Zn in G. grapsus. All Hg analyzes performed were below the method quantification limit (17.7 µg kg-1). The metals and semimetals showed similar results to studies conducted in other regions.
31
Medeiros, Fabio Henrique [UNESP]. "Caracterização da deposição atmosférica e aporte de espécies químicas no principal corpo aquático da cidade de São José do Rio Preto, SP." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/97770.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:29:06Z (GMT). No. of bitstreams: 0
Previous issue date: 2011-04-29Bitstream added on 2014-06-13T20:59:12Z : No. of bitstreams: 1
medeiros_fh_me_sjrp.pdf: 1798469 bytes, checksum: 494d9fc9ab81d5ac6ffcb3813a9a357c (MD5)<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>A atmosfera tem grande importância no transporte e distribuição de elementos oriundos de atividades naturais ou antrópicas, sobre a superfície terrestre, sendo a deposição atmosférica o principal processo de ciclagem dos compostos químicos entre os compartimentos ambientais. A cidade de São José do Rio Preto (SJRP) possui um pequeno parque industrial, conta com a presença de duas rodovias de grande tráfego, a rodovia Washington Luís (SP-310) e a rodovia Transbrasiliana (BR-153), e em termos agrícolas a região é responsável por 12% da produção de etanol do estado, e destacando-se também, em menor quantidade, o cultivo da laranja e de pastagens. Neste contexto o objetivo deste trabalho foi a caracterização de espécies químicas na deposição atmosférica total (DT) e deposição atmosférica apenas úmida (DU) da cidade de SJRP visando avaliar a contribuição da mesma como fonte destes compostos para o rio Preto. Um total de 103 amostras de DT e 96 de DU foram coletadas para o período de março de 2009 a setembro de 2010. A amostragem, preservação e quantificação de Al, Sb, As, Ba, Cd, Cu, Pb, Cr, Ni, Zn, K+, NH4 +, PO4 3-, NO3 -, SO4 2-, pH, C.E. e TOC (Carbono Orgânico Total) foram realizadas seguindo recomendações de métodos oficiais. Os resultados obtidos e expressos como média ponderada pelo volume (MPV) para as amostras de DT e de DU foram maiores no período de safra da cana-de-açúcar para Ni (0,53 e 0,44 µg L-1), Al (63 e 28 µg L-1), Pb (0,88 e 0,66 µg L-1), Ba (4,67 e 3,20 µg L-1), Zn (9,21 e 5,50 µg L-1), K+ (0,68 e 0,17 mg L-1), NH4 + (1,31 e 0,38 mg L-1), SO4 2- (5,99 e 4,70 mg L-1), PO4 3- (3,08 e 0,48 mg L-1) e NO3 - (0,94 e 0,40 mg L-1). Destaca-se para o Cr a maior MPV nas amostras de DT também no período de safra da cana-de-açúcar (0,33 µg L-1), já para as amostras de DU o valor de MPV para ambos os períodos...<br>The atmosphere plays a very important role in transport and distribution of elements from natural and anthropogenic activities on the earth. The atmospheric deposition is the main process through which chemical compounds present in the atmosphere can be reintroduced to other environmental compartments. The city of São José do Rio Preto (SJRP) has a small industrial park, and two highways, Washington Luís (SP-310) and Transbrasiliana (Br-153), and in agricultural terms it is responsible for 12% of the ethanol production in the state of São Paulo, and in smaller proportion stand the orange crop and pasture. In this context the objective of this work was the characterization of the chemical species in the bulk (BD) and wet only (WD) deposition of SJRP city to evaluate the contribution of deposition as a diffuse source of compounds for the Preto river. A total of 103 bulk and 96 wet-only samples were collected for the period of March 2009 to September 2010. The sampling, preservation and quantification of Al, Sb, As, Ba, Cd, Cu, Pb, Cr, Ni, K e Zn, NH4 +, PO4 3-, NO3 -, SO4 2-, pH, E.C. and TOC were performed in accordance with official methods recommendations. The results obtained and expressed as volume-weighted mean concentration (VWM) was higher for the sugar cane harvest period for BD and WD for Ni (0.53 and 0.44 µg L-1), Al (63 and 28 µg L-1), Pb (0.88 and 0.66 µg L-1), Ba (4.67 and 3.20 µg L-1), Zn (9.21 and 5.50 µg L-1), K+ (0.68 and 0.17 mg L-1), NH4 + (1.31 and 0.38 mg L-1), SO4 2- (5.99 and 4.70 mg L-1), PO4 3- (3.08 and 0.48 mg L-1) and NO3 - (0.94 and 0.40 mg L-1). The highest Cr VWM (0.33 µg L-1) in the bulk samples was also observed for the sugar cane harvest period, but with regard to the WOD samples the VWM for both periods was the same (0.13 µg L-1). For Cu, TOC and NPOC the highest VWM was observed for the sugar cane harvest period, for the BD samples... (Complete abstract click electronic access below)
32
Huang, Minjuan. "Risk assessments of human exposure to metal(loid)s via urban dust and airborne particles in Guangzhou, South China." HKBU Institutional Repository, 2013. http://repository.hkbu.edu.hk/etd_ra/1494.
Full text
33
Gállová, Eva. "Stanovení polokovových prvků v potravinách." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2011. http://www.nusl.cz/ntk/nusl-216751.
Full textAbstract:
This diploma thesis deals with an optimization technique for the determination of semimetals in selected samples of food, which consists of sample digestion, preconcentration and detection of the elements. Preconcentration is usually chosen because these elements are contained in foods only in trace amounts, which are undetectable for some techniques. This work also made characteristics of semimetals, in terms of their functions in the body, of the occurrence in food and the consequences for the organism on their surplus or shortage. The chosen technique of preconcentration in this work was the preconcentration of titanium dioxide. When optimizing the techniques, however, was unlike the results published in literature, obtained low yield of elements sorbed on titanium dioxide, therefore the samples were measured by inductively coupled plasma mass spectrometry directly after their mineralization, wet digestion with low temperature. The results of this work indicate that the elements arsenic, boron and selenium are given technique detectable without preconcentration, whilst set germanium content in all samples failed, due to very low concentrations and therefore in these cases would be required preconcentration.
34
Naozuka, Juliana. "Especiação química elementar em castanha-do-pará, coco e cupuaçu." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/46/46133/tde-19122008-140514/.
Full textAbstract:
Nesse trabalho foram realizados estudos para o fracionamento e especiação de Cu, Fe, Mn, Se e Zn em castanha-do-pará (Bertholletia excelsa H. B. K), polpa de coco (Cocos nucifera L.) e semente de cupuaçu (Theobroma grandiflorum). A extração seqüencial sólido-líquido combinada com GF AAS foi utilizada para o fracionamento e determinação dos elementos associados às frações proteicas. As concentrações de proteínas encontradas nos extratos de castanha-do-pará (6 a 76 mg g-1) foram maiores do que aquelas encontradas nos extratos de semente de cupuaçu (2 a 27 mg g-1) e de polpa de coco (1 a 12 mg g-1). A preliminar relação de Cu, Fe, Mn, Se e Zn associado a diferentes grupos de proteínas foi observada, indicando a possível interação desses elementos com albuminas, globulinas, prolaminas e glutelínas. O acoplamento on-line SEC-UV e off-line SEC-UV GFAAS foi aplicado com sucesso para a identificação das espécies de Cu, Fe, Mn, Se e Zn nos extratos de água, NaCl e NaOH de castanha-do-pará, polpa de coco e semente de cupuaçu. Em geral, os elementos de interesse encontram-se associados a espécies de pesos moleculares inferiores a 13 kDa nos extratos de água e NaCl e a 28 kDa nos extratos de NaOH. A combinação das informações obtidas desse acoplamento com os espectros de massas do MALDI-TOF da castanha-do-pará confirmam a associação de Cu, Fe, Mn, Se e Zn com duas espécies presentes no extrato de água de 6 kDa (Fe, Mn and Zn) e 11 kDa (Cu, Mn and Se).<br>In this work, studies were done for the fractionation and speciation of Cu, Fe, Mn, Se and Zn in Brazil-nut (Bertholletia excelsa H.B.K.), cupuassu (Theobroma grandiflorum) seeds and coconut (Cocos nucifera L.) pulp. The sequential solid-liquid extraction combined with GF AAS was used to fractionation and determination of elements associated to proteins fractions. The determined protein concentrations in extractants of Brazil-nut (6 a 76 mg g-1) are higher than those observed for extractants of cupuassu seeds (2 a 27 mg g-1) and coconut pulp (1 a 12 mg g-1). The preliminary relationship of Cu, Fe, Mn, Se and Zn associated to different proteins groups was observed, indicating a possible interation of these elements with albumins, globulins, prolamins and glutelins. The on-line SEC-UV and off-line SEC-UV GFAAS hyphenation was applied with sucess for the identification of Cu, Fe, Mn, Se and Zn species in the water, NaCl and NaOH extractants of Brazil-nut, cupuassu seeds and coconut pulp. In general, the interest elements were found associated to species of molecular weights lower than 13 kDa for water and NaCl extractants and 28 kDa for NaOH extractants. The combination of the informations of this hyphenation with MALDI-TOF mass spectra of the Brazil-nut gave confirmation of the association of the Cu, Fe, Mn, Se and Zn with two water-soluble species of 6 kDa (Fe, Mn and Zn) and 11 kDa (Cu, Mn and Se).
35
Behrends, Jan [Verfasser], Jens H. [Akademischer Betreuer] Bardarson, Jens H. [Gutachter] Bardarson, Roderich [Gutachter] Moessner, and Carsten [Gutachter] Timm. "Transport and Quantum Anomalies in Topological Semimetals / Jan Behrends ; Gutachter: Jens H. Bardarson, Roderich Moessner, Carsten Timm ; Betreuer: Jens H. Bardarson." Dresden : Technische Universität Dresden, 2019. http://d-nb.info/1226897495/34.
Full text
36
Rauch, Tomáš Verfasser], Ingrid [Akademischer Betreuer] [Mertig, Steffen [Akademischer Betreuer] Trimper, and Markus [Akademischer Betreuer] Donath. "Topological insulators and semimetals : theory for bulk and surface electronic properties : [kumulative Dissertation] / Tomáš Rauch ; Ingrid Mertig, Steffen Trimper, Markus Donath." Halle, 2016. http://d-nb.info/1116952483/34.
Full text
37
Medeiros, Fabio Henrique. "Caracterização da deposição atmosférica e aporte de espécies químicas no principal corpo aquático da cidade de São José do Rio Preto, SP /." São José do Rio Preto : [s.n.], 2011. http://hdl.handle.net/11449/97770.
Full textAbstract:
Orientador: Marcia Cristina Bisinoti<br>Banca: Pedro Sergio Fadini<br>Banca: Mauricio Boscolo<br>Resumo: A atmosfera tem grande importância no transporte e distribuição de elementos oriundos de atividades naturais ou antrópicas, sobre a superfície terrestre, sendo a deposição atmosférica o principal processo de ciclagem dos compostos químicos entre os compartimentos ambientais. A cidade de São José do Rio Preto (SJRP) possui um pequeno parque industrial, conta com a presença de duas rodovias de grande tráfego, a rodovia Washington Luís (SP-310) e a rodovia Transbrasiliana (BR-153), e em termos agrícolas a região é responsável por 12% da produção de etanol do estado, e destacando-se também, em menor quantidade, o cultivo da laranja e de pastagens. Neste contexto o objetivo deste trabalho foi a caracterização de espécies químicas na deposição atmosférica total (DT) e deposição atmosférica apenas úmida (DU) da cidade de SJRP visando avaliar a contribuição da mesma como fonte destes compostos para o rio Preto. Um total de 103 amostras de DT e 96 de DU foram coletadas para o período de março de 2009 a setembro de 2010. A amostragem, preservação e quantificação de Al, Sb, As, Ba, Cd, Cu, Pb, Cr, Ni, Zn, K+, NH4 +, PO4 3-, NO3 -, SO4 2-, pH, C.E. e TOC (Carbono Orgânico Total) foram realizadas seguindo recomendações de métodos oficiais. Os resultados obtidos e expressos como média ponderada pelo volume (MPV) para as amostras de DT e de DU foram maiores no período de safra da cana-de-açúcar para Ni (0,53 e 0,44 µg L-1), Al (63 e 28 µg L-1), Pb (0,88 e 0,66 µg L-1), Ba (4,67 e 3,20 µg L-1), Zn (9,21 e 5,50 µg L-1), K+ (0,68 e 0,17 mg L-1), NH4 + (1,31 e 0,38 mg L-1), SO4 2- (5,99 e 4,70 mg L-1), PO4 3- (3,08 e 0,48 mg L-1) e NO3 - (0,94 e 0,40 mg L-1). Destaca-se para o Cr a maior MPV nas amostras de DT também no período de safra da cana-de-açúcar (0,33 µg L-1), já para as amostras de DU o valor de MPV para ambos os períodos... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: The atmosphere plays a very important role in transport and distribution of elements from natural and anthropogenic activities on the earth. The atmospheric deposition is the main process through which chemical compounds present in the atmosphere can be reintroduced to other environmental compartments. The city of São José do Rio Preto (SJRP) has a small industrial park, and two highways, Washington Luís (SP-310) and Transbrasiliana (Br-153), and in agricultural terms it is responsible for 12% of the ethanol production in the state of São Paulo, and in smaller proportion stand the orange crop and pasture. In this context the objective of this work was the characterization of the chemical species in the bulk (BD) and wet only (WD) deposition of SJRP city to evaluate the contribution of deposition as a diffuse source of compounds for the Preto river. A total of 103 bulk and 96 wet-only samples were collected for the period of March 2009 to September 2010. The sampling, preservation and quantification of Al, Sb, As, Ba, Cd, Cu, Pb, Cr, Ni, K e Zn, NH4 +, PO4 3-, NO3 -, SO4 2-, pH, E.C. and TOC were performed in accordance with official methods recommendations. The results obtained and expressed as volume-weighted mean concentration (VWM) was higher for the sugar cane harvest period for BD and WD for Ni (0.53 and 0.44 µg L-1), Al (63 and 28 µg L-1), Pb (0.88 and 0.66 µg L-1), Ba (4.67 and 3.20 µg L-1), Zn (9.21 and 5.50 µg L-1), K+ (0.68 and 0.17 mg L-1), NH4 + (1.31 and 0.38 mg L-1), SO4 2- (5.99 and 4.70 mg L-1), PO4 3- (3.08 and 0.48 mg L-1) and NO3 - (0.94 and 0.40 mg L-1). The highest Cr VWM (0.33 µg L-1) in the bulk samples was also observed for the sugar cane harvest period, but with regard to the WOD samples the VWM for both periods was the same (0.13 µg L-1). For Cu, TOC and NPOC the highest VWM was observed for the sugar cane harvest period, for the BD samples... (Complete abstract click electronic access below)<br>Mestre
38
Möckel, Sebastian [Verfasser], Martin [Gutachter] Ammon, Johanna [Gutachter] Erdmenger, and Dias Oscar [Gutachter] Campos. "Numerical studies of higher-dimensional localized black holes and holographic Weyl semimetals / Sebastian Möckel ; Gutachter: Martin Ammon, Johanna Erdmenger, Oscar Campos Dias." Jena : Friedrich-Schiller-Universität Jena, 2018. http://d-nb.info/117220683X/34.
Full text
39
Yang, Shuo-Ying [Verfasser], Stuart S. P. [Gutachter] Parkin, Ingrid [Gutachter] Mertig, and Vitto Zheng [Gutachter] Han. "In search of extraordinary Hall effects in topological semimetals / Shuo-Ying Yang ; Gutachter: Stuart S. P. Parkin, Ingrid Mertig, Vitto Zheng Han." Halle (Saale) : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2020. http://d-nb.info/1222513757/34.
Full text
40
Lau, Alexander [Verfasser], Jeroen van den [Akademischer Betreuer] Brink, Jeroen van den [Gutachter] Brink, and Carmine [Gutachter] Ortix. "Symmetry-enriched topological states of matter in insulators and semimetals / Alexander Lau ; Gutachter: Jeroen van den Brink, Carmine Ortix ; Betreuer: Jeroen van den Brink." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://d-nb.info/1154680487/34.
Full text
41
Watzman, Sarah June. "Thermal Energy Conversion Utilizing Magnetization Dynamics and Two-Carrier Effects." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523621461827864.
Full text
42
Noky, Jonathan [Verfasser], Claudia [Gutachter] Felser, Claudia [Akademischer Betreuer] Felser, Jeroen van den [Gutachter] Brink, and Jürgen [Gutachter] Kübler. "Anomalous electric, thermal, and thermoelectric transport in magnetic topological metals and semimetals / Jonathan Noky ; Gutachter: Claudia Felser, Jeroen van den Brink, Jürgen Kübler ; Betreuer: Claudia Felser." Dresden : Technische Universität Dresden, 2021. http://d-nb.info/123917702X/34.
Full text
43
RIBEIRO, ANDREZA P. "Determinacao de metais pesados e outros elementos de interesse em sedimentos lacustres da Estacao de Tratamento de Esgoto de Barueri, Sao Paulo, por ativacao neutronica." reponame:Repositório Institucional do IPEN, 2002. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11026.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:47:06Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T14:10:34Z (GMT). No. of bitstreams: 1
08284.pdf: 5015226 bytes, checksum: 6a231582a7866a2856a41c83a5877c9b (MD5)<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>Dissertacao (Mestrado)<br>IPEN/D<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP<br>FAPESP:00/00546-3
44
Kirby, Jason K., and n/a. "Trace metal and metalloid accumulation, distribution, and, speciation in Lake Macquarie, N.S.W., Australia." University of Canberra. Resource, Environmental & Heritage Sciences, 2005. http://erl.canberra.edu.au./public/adt-AUC20051129.124508.
Full textAbstract:
THESIS ORGANISATION
This thesis is organised into nine chapters that include seven international and
national publications (six accepted and one submitted for publication). The initial
overview chapter outlines the justification and direction for this thesis. With the
exception of chapter 8 (accepted for publication on the 1st May 2005); all chapters are
exact duplicates of published articles in international and national refereed journals
(chapters 2 to 7). The initial chapters (2 and 3) presents research findings using a
marine fish species, mullet (Mugil cephalus), to measure trace metal bioavailability in
Lake Macquarie, NSW Australia. While subsequent chapters (4 to 8) are presenting
research under taken to improve the understanding of arsenic cycling in marine and
estuarine environments. The final chapter (chapter 9) is a synopsis of the major
findings presented in this thesis. Due to the publication nature of this thesis, an
unavoidable degree of replication exists within chapters (publications).
45
FAUSTINO, MAINARA G. "Desenvolvimento e validação de metodologia para determinação de metais em amostras de água por espectrometria de emissão óptica com plasma de argônio (ICP-OES)." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/26081.
Full textAbstract:
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-04-08T12:48:16Z
No. of bitstreams: 0<br>Made available in DSpace on 2016-04-08T12:48:16Z (GMT). No. of bitstreams: 0<br>Dissertação (Mestrado em Tecnologia Nuclear)<br>IPEN/D<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
46
MARQUES, JOYCE R. "Otimização e validação de metodologia analítica para determinação de metais e semimetais em efluentes líquidos por espectrometria de emissão óptica com plasma de argônio (ICP-OES)." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/26080.
Full textAbstract:
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-04-08T12:43:32Z
No. of bitstreams: 0<br>Made available in DSpace on 2016-04-08T12:43:32Z (GMT). No. of bitstreams: 0<br>Dissertação (Mestrado em Tecnologia Nuclear)<br>IPEN/D<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
47
Louvet, Thibaud. "Phases relativistes en matière condensée." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN025/document.
Full textAbstract:
Cette thèse porte sur l’étude des cristaux appelés semi-métaux relativistes dans lesquels les électrons se comportent comme des particules relativistes sans masse.Le premier exemple historique d’un tel matériau est le graphène.Dans cet assemblage planaire d’atomes de carbone, les bandes électroniques de valence et de conduction se touchent en deux points distincts du réseau réciproque: il s'agit d'un conducteur de gap nul, un semi-métal.Les électrons proches du niveau de Fermi ont une dynamique relativiste décrite par une équation de Dirac,bien que leur vitesse soit cent fois inférieure à celle de la lumière dans le vide. Des semi-métaux analogues ont récemment été identifiés :les semi-métaux de Weyl et de Dirac à 3D, et des phases plus exotiques décrites par des croisements à plus de deux bandes.Cette diversité de matériaux relativistes pose la question de leurs propriétés communes. Une première partie de la thèse présente les travaux reliés à l’étude de la stabilité de ces phases, c’est à dire du croisement de bandes électroniques. Nous avons étudié cette stabilité d’abord en la reliant à des propriétés topologiques, puis en évaluant l’effet du désordre, tel que des impuretés dans le matériau. Dans la deuxième partie, nous nous intéressons à la manifestation dans le transport de la nature relativiste de ces électrons. Dans une première étude, nous étudions la condition d’existence d’une conductivité finie exactement au croisement des bandes, due à une contribution d’états évanescents. Une deuxième étude porte sur le transport anormal sous champ magnétique dans les semi-métaux de Weyl, comme manifestation de l’anomalie chirale, propriété unique de fermions relativistes<br>This thesis adresses the study of crystals called relativistic semi-metals, in which electrons behave like massless relativistic particles.The first historical example of such a material is graphene.In this planar arrangement of carbon atoms, electronic valence and conduction bands touch at two distincts points in the reciprocal lattice. Thus, graphene is a zero-gap semiconductor, a semi-metal.The dynamics of electrons close to the Fermi level is relativistic, described by a Dirac equation, although their velocity is a hunder times lower than the velocity of light in vacuum. Analogous semi-metallic phases have recently been identified: 3D Weyl and Dirac semimetals, as well as more exotic phases described by crossings with more than two bands. This variety of relativistic materials raises the question of their common properties. A first part of this thesis presents work related to the study of the stability of these phases, i.e. of the electronic band crossing. We have investigated this stability first by relating it to topological properties, then by evaluating the effect of disorder, such as the presence of impurities in the material. In the second part, we focus on the manifestation of the relativistic nature of these electrons in transport. In a first study, we examine the condition of existence of a finite conductivity exactly at the band crossing, due to the contribution of evanescent states. A second study concerns the anomalous transport under a magnetic field in Weyl semi-metals, as a manifestation of the chiral anomaly, a unique property of massless relativistic fermions
48
Radmanesh, Seyed Mohammad Ali. "Ultra-low Temperature Properties of Correlated Materials." ScholarWorks@UNO, 2018. https://scholarworks.uno.edu/td/2511.
Full textAbstract:
Abstract
After the discovery of topological insulators (TIs), it has come to be widely recognized that topological states of matter can actually be widespread. In this sense, TIs have established a new paradigm about topological materials. Recent years have seen a surge of interest in topological semimetals, which embody two different ways of generalizing the effectively massless electrons to bulk materials. Dirac and, particularly, Weyl semimetals should support several transport and optical phenomena that are still being sought in experiments. A number of promising experimental results indicate superconductivity in members of half-Hesuler semimetals which realize the mixing singlet and triplet pairing symmetry. We now turn to results we got through the work on topological semimetals. This work presents quantum high field transports on Dirac and Weyl topological semimetals including Sr1-yMn1-zSb2 (y, z < 0.1), YbMnBi2 and TaP. In case of Sr1-yMn1-zSb2 (y, z < 0.1), massless relativistic fermion was reported with m* = 0.04-0.05m0. This material presented a ferromagnetic order for in 304 K < T < 565 K, but a canted antiferromagnetic order with a net ferromagnetic component for T < 304 K. These are considered striking features of Dirac fermions For YbMnBi2, we reported the unusual interlayer quantum transport behavior in magnetoresistivity, resulting from the zeroth LL mode observed in this time reversal symmetry breaking type II Weyl semimetal. Also, for Weyl semimetal TaP the measurements probed multiple Fermi pockets, from which nontrivial π Berry phase and Zeeman splitting were extracted. Our ultra-low penetration depth measurements on half-Heuslers YPdBi and TbPdBi revealed a power- law behavior with n= 2.76 ± 0.04 for YPdBi samples and n=2.6 ± 0.3 for TbPdBi sample. We may conclude the exponent n > 2 implies nodless superconducting gap in our samples. Also, we found that despite the increase in magnetic correlations from YPdBi to TbPdBi, superconductivity remains robust in both systems which indicates that AF fluctuations do not play a major role in superconducting mechanism.
49
Mizobata, William Nobuhiro. "Interação entre impurezas enterradas em um semimetal de Weyl : caso magnético /." Ilha Solteira, 2019. http://hdl.handle.net/11449/181343.
Full textAbstract:
Orientador: Antônio Carlos Ferreira Seridonio<br>Resumo: Investigamos teoricamente um sistema composto por duas impurezas afastadas e enterradas em um semimetal de Weyl. Analisamos a densidade de estados local para duas situações: com simetrias de reversão temporal e inversão preservadas e; simetria de reversão temporal quebrada e inversão preservada. Na situação em que as duas simetrias são preservadas, o Hamiltoniano descreve um semimetal de Dirac. Sendo assim, verificamos a densidade de estados local em dois pontos diferentes do semimetal de Dirac e os orbitais moleculares formado pelas impurezas. É possível observar que em alguns pontos, a densidade de estados total, que pode ser obtido experimentalmente via espectroscopia de varredura por tunelamento, há a presença de apenas dois picos, enquanto que em outro ponto há a presença de quatro picos. Sendo assim, a presença de dois picos nos leva a crer que não há interação entre as impurezas, entretanto, em outro ponto que contém quatro picos em sua densidade de estados, mostra que há interação entre as impurezas. Analisamos os orbitais moleculares realizando uma topografa espacial da densidade de estados e é possível observar estados ligante e antiligante entre as impurezas com orbitais s. A segunda situação, com a quebra de simetria de reversão temporal e simetria de inversão preservada, temos um semimetal de Weyl com as bandas de energias separadas no espaço dos momentos e com energias degeneradas. Verificamos na densidade de estados local, uma magnetização das impurezas devido ... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: We investigate theoretically the setup composed by two distant impurities and burried in Weyl semimetal. We analyze a local density of states for two situations: with time reversal symmetry and inversion symmetry preserved and; time reversal symmetry broken and inversion symmetry preserved. In the situation that the two symmetries are preserved, the Hamiltonian describes a Dirac semimetal. Therefore, we verified the local density of states in two different points of Dirac semimetal and the molecular orbital formed by the impurities. It is possible to observe that in some points, the total density of states, which can be obtained experimentally via scanning tunneling microscope, there is the presence of just two peaks, while that in another point there is the presence of four peaks. Therefore, the presence of two peaks leads us to belive that there is no interaction between impurities, however, in the another point that contain four peaks in the density of states, show that there is interaction between the impurities. We analyze the molecular orbital realizing a spacial topography of density of states and it is possible to observe bonding and antibonding states between impurities with s orbital. The second situation, with the time reversal symmetry broken and inversion symmetry preserved, we have a Weyl semimetal with separated energy bands in momentum space and degenerate energy. We verified in the local density of states, a magnetization of the impurities due to the time rev... (Complete abstract click electronic access below)<br>Mestre
50
Báring, Luís Augusto Gomes 1983. "Supercondutividade em semimetais e isolantes topológicos." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277009.
Full textAbstract:
Orientador: Iakov Veniaminovitch Kopelevitch<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin<br>Made available in DSpace on 2018-08-22T01:33:07Z (GMT). No. of bitstreams: 1
Baring_LuisAugustoGomes_D.pdf: 21081310 bytes, checksum: 275f0ba5ff80d6f9f19f53cf8316e1a6 (MD5)
Previous issue date: 2012<br>Resumo: No presente trabalho estudamos os semimetais bismuto Bi, antimônio Sb e Bi1-xSbx, materiais com propriedades topologicamente não triviais. Observamos a ocorrência de supercondutividade intrínseca em bismuto com TC »= 8:5K. Construímos, a partir dos dados de magnetização e resistência, o diagrama de fase do campo crítico H versus a temperatura T. Esse diagrama de fase, pode ser ajustado segundo modelos da literatura válidos para supercondutividade granular. Detectamos, no bismuto, o aumento da corrente Josephson e acoplamento intergranular no limite quântico devidos à quantização de Landau. Isso se manifesta como uma supercondutividade reentrante. Foi também encontrada transição tipo metal-isolante induzida por campo magnético em todos os materiais estudados. O diagrama de fase H versus T mostra uma extraordinária semelhança entre os três materiais. A amostra Bi1-xSbx, com x = 0:052, revelou a ocorrência de transição semimetal-isolante topológico já em campo magnético zero. Fizemos uma comparação com resultados anteriores da literatura, analisando a dependência da temperatura em que ocorre essa transição em relação à concentração de antimônio x e ao campo magnético B e demonstramos a similaridade entre eles. Observamos, também, supercondutividade nos semimetais bismuto, antimônio e no Bi1-xSbx, induzida por dopagem com os metais ouro e índio, e mostramos que a supercondutividade está associada à interface entre os metais e os semimetais. Finalmente, encontramos a indução de supercondutividade mediante a aplicação de campo magnético em bismuto, consistente com a ocorrência de férmions de Majorana na interface entre esse material e a tinta prata usada para os contatos. Tal observação pode ser devida, também, à ocorrência de um estado supercondutor fora do equilíbrio.<br>Abstract: In this work we studied the semimetals bismuth Bi, antimony Sb and Bi1-xSbx, all of them with non-trivial topologic properties. We observed an intrinsic superconductivity in bismuth, with TC »= 8:5 K. The phasediagram of the critical field H versus the temperature T, based upon the magnetization and resistance data, may be well fitted according to theoretical models valid for granular superconductivity. We also detected, in bismuth, the increase of the Josephson current and interganular coupling in the quantum limit due to Landau quantization. This manifests itself as a reentrant superconducting state. Our results revealed a metal-insulator transition triggered by magnetic field, for all the studied materials. The phase diagram H ¡T shows a striking similarity between them. The sample Bi1-xSbx with x = 0:052 demonstrated a semimetal-insulator transition even at zero field. We compared our results with previous results of other groups and analyzed the temperature dependence of the transition as a function of the antimony amount x and the magnetic field B and demonstrated their similarity. We also observed supeerconductivity in the semimetals bismuth, antimony and Bi1-xSbx, triggered by doping with the metals gold and indium, and showed that the superconductivity is associated to the interface between the metals and the semimetals. Finally, we found the superconductivity induced by the aplication of magnetic field in bismuth, consistent with the Majorana fermions present in the interface between this material and the silver paste contacts. This may also be related to a non-equilibrium superconduting state.<br>Doutorado<br>Física<br>Doutor em Ciências