Дисертації з теми "Topological surface states"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-19 дисертацій для дослідження на тему "Topological surface states".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
Pantaleon, Peralta Pierre Anthony. "A theoretical investigation of 2D topological magnets." Thesis, University of Manchester, 2019. https://www.research.manchester.ac.uk/portal/en/theses/a-theoretical-investigation-of-2d-topological-magnets(1a330443-752a-4a41-b866-72f7a98c97a5).html.
Повний текст джерелаKunst, Flore Kiki. "Topology Meets Frustration : Exact Solutions for Topological Surface States on Geometrically Frustrated Lattices." Licentiate thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-150281.
Повний текст джерелаZhou, Wenwen. "STM probe on the surface electronic states of spin-orbit coupled materials." Thesis, Boston College, 2014. http://hdl.handle.net/2345/bc-ir:103564.
Повний текст джерелаSpin-orbit coupling (SOC) is the interaction of an electron's intrinsic angular momentum (spin) with its orbital momentum. The strength of this interaction is proportional to Z4 where Z is the atomic number, so generally it is stronger in atoms with higher atomic number, such as bismuth (Z=83) and iridium (Z=77). In materials composed of such heavy elements, the prominent SOC can be sufficient to modify the band structure of the system and lead to distinct phase of matter. In recent years, SOC has been demonstrated to play a critical role in determining the unusual properties of a variety of compounds. SOC associated materials with exotic electronic states have also provided a fertile platform for studying emergent phenomena as well as new physics. As a consequence, the research on these interesting materials with any insight into understanding the microscopic origin of their unique properties and complex phases is of great importance. In this context, we implement scanning tunneling microscopy (STM) and spectroscopy (STS) to explore the surface states (SS) of the two major categories of SOC involved materials, Bi-based topological insulators (TI) and Ir-based transition metal oxides (TMO). As a powerful tool in surface science which has achieved great success in wide variety of material fields, STM/STS is ideal to study the local density of states of the subject material with nanometer length scales and is able to offer detailed information about the surface electronic structure. In the first part of this thesis, we report on the electronic band structures of three-dimensional TIs Bi2Te3 and Bi2Se3. Topological insulators are distinct quantum states of matter that have been intensely studied nowadays. Although they behave like ordinary insulators in showing fully gapped bulk bands, they host a topologically protected surface state consisting of two-dimensional massless Dirac fermions which exhibits metallic behavior. Indeed, this unique gapless surface state is a manifestation of the non-trivial topology of the bulk bands, which is recognized to own its existence to the strong SOC. In chapter 3, we utilize quasiparticle interference (QPI) approach to track the Dirac surface states on Bi2Te3 up to ~800 meV above the Dirac point. We discover a novel interference pattern at high energies, which probably originates from the impurity-induced spin-orbit scattering in this system that has not been experimentally detected to date. In chapter 4, we discuss the topological SS evolution in (Bi1-xInx)2Se3 series, by applying Landau quantization approach to extract the band dispersions on the surface for samples with different indium content. We propose that a topological phase transition may occur in this system when x reaches around 5%, with the experimental signature indicating a possible formation of gapped Dirac cone for the surface state at this doping. In the second part of this thesis, we focus on investigating the electronic structure of the bilayer strontium iridate Sr3Ir2O7. The correlated iridate compounds belong to another domain of SOC materials, where the electronic interaction is involved as well. Specifically, the unexpected Mott insulating state in 5d-TMO Sr2IrO4 and Sr3Ir2O7 has been suggested originate from the cooperative interplay between the electronic correlations with the comparable SOC, and the latter is even considered as the driving force for the extraordinary ground state in these materials. In chapter 6, we carried out a comprehensive examination of the electronic phase transition from insulating to metallic in Sr3Ir2O7 induced by chemical doping. We observe the subatomic feature close to the insulator-to-metal transition in response with doping different carriers, and provide detailed studies about the local effect of dopants at particular sites on the electronic properties of the system. Additionally, the basic experimental techniques are briefly described in chapter 1, and some background information of the subject materials are reviewed in chapter 2 and chapter 5, respectively
Thesis (PhD) — Boston College, 2014
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
O'Neill, Christopher David. "Topological properties of SnTe and Fe3Sn2." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20391.
Повний текст джерелаLau, 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.
Повний текст джерелаBerntsen, Magnus H. "Consequences of a non-trivial band-structure topology in solids : Investigations of topological surface and interface states." Doctoral thesis, KTH, Material- och nanofysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121974.
Повний текст джерелаQC 20130507
Scholz, Markus Reiner [Verfasser], and Oliver [Akademischer Betreuer] Rader. "Spin polarization, circular dichroism, and robustness of topological surface states : a photoemission study / Markus Reiner Scholz ; Betreuer: Oliver Rader." Potsdam : Universität Potsdam, 2012. http://d-nb.info/1218400889/34.
Повний текст джерелаMandal, Partha Sarathi [Verfasser], Oliver [Akademischer Betreuer] Rader, Hans-Joachim [Gutachter] Elmers, and Martin [Gutachter] Weinelt. "Controlling the surface band gap in topological states of matter / Partha Sarathi Mandal ; Gutachter: Hans-Joachim Elmers, Martin Weinelt ; Betreuer: Oliver Rader." Potsdam : Universität Potsdam, 2020. http://d-nb.info/1221183621/34.
Повний текст джерелаLambert, Fabian [Verfasser], Ilya [Gutachter] Eremin, and Konstantin [Gutachter] Efetov. "Investigation of surface states in topological Weyl semi-metals and Weyl superconductors / Fabian Lambert ; Gutachter: Ilya Eremin, Konstantin Efetov ; Fakultät für Physik und Astronomie." Bochum : Ruhr-Universität Bochum, 2019. http://d-nb.info/1189421887/34.
Повний текст джерелаTchoumakov, Sergueï. "Signatures relativistes en spectroscopie de matériaux topologiques : en volume et en surface." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS258/document.
Повний текст джерелаDuring my PhD studies I focused on the relativistic properties of threedimensional topological materials, namely Weyl semimetals and topological insulators. After introducing surface states and topological materials I discuss their covariance in trigonometric and hyperbolic rotations. These transformations help to solve the equations of motion of an electron in a magnetic field or at the surface with an applied electric field or with a tilt in the band dispersion. In a first place, I illustrate these transformations for the magneto-optical response of tilted Weyl semimetals. This work is related to my collaboration with experimentalists at LNCMI, Grenoble for characterizing the band structure of Cd₃As₂ where we show that this material is a Kane semi-metal instead of a Dirac semi-metal in the experimentally accessible range of chemical doping. The other part of this thesis is concerned with the surface states of topological insulators. I show that massive surface states can also exist in addition to the chiral surface state due to band inversion. Such states may have already been observed in ARPES measurement of oxidized Bi₂Se₃ and Bi₂Te₃ and in transport measurement of strained bulk HgTe. I show the work we performed with experimentalists at LPA, Paris on the behavior of HgTe surface states for strong field effects. Finally, I discuss the states at the interface of a Weyl semimetal and a small gap insulator. In this situation, an applied magnetic field or the tilt of the band dispersion can strongly affect the observed surface states
Wang, Wei. "Manipulation of Lamb waves with elastic metamaterials." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS414.
Повний текст джерелаWe develop elastic pillared metamaterials to manipulate Lamb waves. Firstly, the negative properties associated with bending, compression and torsion resonances in two structures consisting of pillars on one side of a thin plate are examined. We describe in details two different mechanisms at the origin of doubly negative property. The potential of these structures for negative refraction of Lamb waves and acoustic cloaking is demonstrated numerically. Secondly, we present the topologically protected transport of Lamb waves by analogy with quantum spin and valley quantum Hall effects. By rearranging the previous structures into a honeycomb network, a single Dirac cone and a double Dirac cone are introduced. We discuss the appearance of topologically valley-protected edge states in an asymmetrical double-sided pillar structure. The unidirectional propagation of edge states on different domain walls is studied. In addition, we consider a symmetrical double-sided system allowing the separation of the symmetric and antisymmetric modes. Combined edge states protected topologically by pseudospin and pseudospin-valley degree of freedom are demonstrated. Third, we propose an approach to actively control the transmission of the antisymmetric Lamb wave propagating through an infinite line of pillars. Two different situations with bending and compression resonances respectively separated or superimposed are studied. External tensile force and pressure are applied to the pillars, which allows them to couple with the bending and compressive vibrations. The transmission is studied as a function of the amplitude and the relative phase of the external sources
Barbedienne, Quentin. "Étude d'états de surface topologiques en vue de leur intégration dans des dispositifs d'électronique de spin." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS524/document.
Повний текст джерелаConventional spintronics generally uses magnetic materials to produce a spin current from a current of charge. Another means, more recently studied, is the use of spin-orbit coupling (SOC). It makes possible to produce a pure current of spin in a direction transverse to the charge current, taking into account the principles of relativistic quantum mechanics. In materials with strong spin-orbit coupling, the spin currents are large enough to imagine using them for magnetic switching in spintronic devices. The spin-orbit coupling, corresponding to a relativistic correction in the equations of motion of the electron, a spin 1/2 particle, can be large in materials containing heavy atoms. This means that a conversion from charge current to spin current can be obtained using the properties of SOC systems such as platinum (Pt), tungsten(W) or tantalum (Ta) for example. Recently 2 dimensionnal electronic gas (2DEG), obtained at particular interfaces or surfaces, have demonstrated properties allowing particularly effective inter-conversion effects. In particular Rashba states or topological insulator systems, are currently arousing a strong interest in the spintronics community for this faculty of spin-charge conversion.In this particular context, over the last ten years or so, topological insulators have been studied for their electronic properties which are rooted in the theoretical definition of the integer quantum Hall effect given by Thouless, as well as in the work of Haldane in graphene and Kane in low bandgap semiconductor systems with a strong SOC. These systems have intriguing electrical properties: they are insulating in volume and conductive on the surfaces. These conductivity states have a linear energy dispersion as a function of the k-wave vector, as in the case of the graphene, with a determined spin helicity.Nevertheless, many questions remain open as the understanding of the mechanisms at the origin of these states of surface conduction, but also as to the simplest way to detect these topological states. In order to integrate in spintronic devices and to realize TI/Ferromagnetic materials interface, a number of questions arise: how to preserve the nature of the topological states at the interface? What materials should be used and what is the atomic nature of the interface (inter-mixing) ? What are the electronic exchanges at the interface? Etc.One of the applications using the properties of topological insulators, is to use the conversion properties of the charge current to spin current in order to modify or switch the magnetization of a ferromagnetic element or memory deposited directly (or separated by a buffer layer) on the topological material itself. Such a two-layer system or multilayer should be capable of integration into a magnetic random access memory (MRAM) or of increasing the potential of disks (SSD) due to the permanent and non-volatile nature of the magnetisation state of the material. This is framework of this thesis
Guan, Syu-You, and 關旭佑. "Superconducting topological surface states in thenoncentrosymmetric bulk superconductor PbTaSe2." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/gx33b5.
Повний текст джерела國立臺灣大學
物理學研究所
105
In this thesis, we first introduce the previous study of topological insulator and the topological superconductor. The discovery of topological insulator (TI) is a recent breakthrough of physics. The topological protect surface in TI, forbidden the backscattering of electrons, gives new transport properties of the material. Combining the superconductor with the topological properties may host a type of new material called topological superconductor (TSC). The search for TSCs is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exist the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level (EF) combined with fully gapped bulk superconductivity. In the second chapter, we introduce the construction of an ultra-low-temperature (ULT) high-magnetic-field (HF) ultra-high-vacuum (UHV) scanning tunneling microscope. Sub-Kelvin temperature and strong field advance the ability of instrument in research. UHV environment keeps cleanness of the sample during the study. Such instrument working in three extreme environments needs to state-of –the-art design with the careful operation. The test result shows the STM has high resolution in energy and space. In the third chapter, we report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe2. Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point at E ≅ 1.0 eV, of which the inner TSS and the partial outer TSS cross EF on the Pb-terminated surface. With sub-Kelvin energy resolution achieved in the ULT-HF-UHV STM, the fully superconducting gap of PbTaSe2 is clearly resolved, which suggests the TSS gapped out at EF. The tunneling conductance map shows the vortex is presented under the magnetic field, and zero energy conductance peak is observed at vortex core. This discovery reveals PbTaSe2 as a promising candidate for TSC. Lastly, the future improvement of the instrument and further study for PbTaSe2 are introduced. Increasing the holding time at 4 K and investigate the pairing mechanism are priorities. Keyword: Topological superconductor, topological insulator, Majorana fermion, scanning tunneling microscope, PbTaSe2
Andrade, Erick Fernando. "Visualizing Quasiparticle Scattering of Nematicity in NaFeAs and of Topological Surface States in MoTe2." Thesis, 2018. https://doi.org/10.7916/D854452F.
Повний текст джерелаLau, Alexander. "Symmetry-enriched topological states of matter in insulators and semimetals." Doctoral thesis, 2017. https://tud.qucosa.de/id/qucosa%3A30848.
Повний текст джерелаSlobozhaniuk, Aleksei. "Manipulating Electromagnetic Fields with Advanced Metamaterials." Phd thesis, 2017. http://hdl.handle.net/1885/136604.
Повний текст джерелаWei, Chih-Kuang, and 魏志光. "Experimentally Demonstrate the Surface State and Optical Topological Phase Transition of One Dimensional Hyperbolic Metamaterials." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/n82dx9.
Повний текст джерела國立清華大學
材料科學工程學系
105
The optical responses of one dimensional hyperbolic metamaterials (1DHMMs) are usually determined by effective medium theory based on the long wavelength approximation. However, the long wavelength approximation shows significant deviation when the wavelength of the incident light is comparable with the unit cell of HMMs. Therefore, plasmonic band theory have been suggested to analyze the 1DHMMs recently and the existence of the interface state has been proposed. The requirement for the existence of the interface state is determined by the admittance matching condition. Furthermore, the interface state formation in the plasmonic band gap can be related to the properties of the plasmonic band in terms of the wave admittance, so called “bulk-interface correspondence”. In this work, we experimentally identify the existence of the interface state of 1DHMM by the Kretschmann and the Otto configurations. By varying the metallic filling ratio in the 1DHMMs, we successfully demonstrate the disappearance and reappearance of the interface state which indicates the optical topological phase transition of 1DHMMs.
Dal, Lago Virginia. "Dirección y manipulación de estados topológicos de la materia. Efectos en grafeno y otros materiales de baja dimensión." Bachelor's thesis, 2017. http://hdl.handle.net/11086/5979.
Повний текст джерелаLos descubrimientos experimentales del grafeno y de los materiales aislantes topológicos han suscitado un gran interés en la comunidad científica. El objetivo de la presente tesis es estudiar los estados topológicos de borde del grafeno y otros materiales de baja dimensión, y analizar diferentes formas de manipulación y dirección de los mismos para obtener sistemas con nuevas propiedades. Para ello, empleamos como base el modelo SSH para polímeros conductores (presenta carácter topológico nativo), y el grafeno. A este último se le inducen propiedades topológicas a partir de perturbaciones externas como ser campos magnéticos, términos de acoplamiento de tipo Haldane o irradiación con luz láser (teoría de Floquet). Entre los resultados encontrados podemos destacar la posibilidad de destruir y crear selectivamente estados de borde topológicos, y de dirigir la corriente eléctrica a través de los mismos. Estos efectos resultan atractivos para el diseño de futuros nanodispositivos y sus posteriores aplicaciones.
The experimental discoveries of graphene and topological insulator materials have aroused great interest in the scientific community. The aim of this thesis is to study the topological edge states of graphene and others low dimensional materials, and to analyze different ways of manipulating and directing them to achieve systems with new properties. In order to do this, we employ the SSH model for conducting polymers (it has a native topological character) and graphene as a base. Topological properties are induced to the latter through external perturbations such as magnetic fields, Haldane coupling terms or irradiation with laser light (Floquet theory). Among the results found we can highlight the possibility of selectively destroying and creating topological edge states, and of directing the electrical current through them. These effects are attractive for the design of future nanodevices and their subsequent applications.
(10203191), Prabhu Kumar Venuthurumilli. "Applications of plasmonics in two dimensional materials & thin films." Thesis, 2021.
Знайти повний текст джерелаThe demand for the faster information transport and better computational abilities is ever increasing. In the last few decades, the electronic industry has met this requirement by increasing the number of transistors per square inch. This lead to the scaling of devices to tens of nm. However, the speed of the electronics is limited to few GHz. Using light, the operating speed of photonic devices can be much larger than GHz. But the photonic devices are diffraction limited and hence the size of photonic device is much larger than the electronic components. Plasmonics is an emerging field with light-induced surface excitations, and can manipulate the light at nanoscale. It can bridge the gap between electronics and photonics.
With the present scaling of devices to few nm, the scientific community is looking for alternatives for continued progress. This has opened up several promising routes recently, including two-dimensional materials, quantum computing, topological computing, spintronics and valleytronics. The discovery of graphene has led to the immense interest in the field of two-dimensional materials. Two dimensional-materials have extraordinary properties compared to its bulk. This work discusses the applications of plasmonics in this emerging field of two-dimensional materials and for heat assisted magnetic recording.
Black phosphorus is an emerging low-direct bandgap two-dimensional semiconductor, with anisotropic optical and electronic properties. It has high mobility and is promising for photo detection at infrared wavelengths due to its low band gap. We demonstrate two different plasmonic designs to enhance the photo responsivity of black phosphours by localized surface plasmons. We use bowtie antenna and bowtie apertures to increase the absorption and polarization selectivity respectively. Plasmonic structures are designed by numerical electromagnetic simulations, and are fabricated to experimentally demonstrate the enhanced photo responsivity of black phosphorus.
Next, we look at another emerging two-dimensional material, bismuth telluride selenide (Bi2Te2Se). It is a topological insulator with an insulating bulk but conducting electronic surface states. These surface states are Dirac like, similar to graphene and can lead to exotic plasmonic phenomena. We investigated the optical properties of Bi2Te2Se and found that the bulk is plasmonic below 650 nm wavelength. We study the distinct surface plasmons arising from the bulk and surface state of the topological insulator, Bi2Te2Se. The propagating surface plasmons at a nanoscale slit in Bi2Te2Se are imaged using near-field scanning optical microscopy. The surface state plasmons are studied with a below band gap excitation of 10.6 µm wavelength and the surface plasmons of the bulk are studied with a visible wavelength of 633 nm. The surface state plasmon wavelength is 100 times shorter than the incident wavelength in sharp contrast to the plasmon wavelength of the bulk.
Next, we look at the application of plasmonics in heat assisted magnetic recording (HAMR). HAMR is one of the next generation data storage technology that can increase the areal density to beyond 1 Tb/in2. Near-field transducer (NFT) is a key component of the HAMR system that locally heats the recording medium by concentrating light below the diffraction limit using surface plasmons. In this work, we use density-based topology optimization for inverse design of NFT for a desired temperature profile in the recording medium. We first perform an inverse thermal calculation to obtain the required volumetric heat generation (electric field) for a desired temperature profile. Then an inverse electromagnetic design of NFT is performed for achieving the desired electric field. NFT designs for both generating a small heated spot size and a heated spot with desired aspect ratio in recording medium are demonstrated. The effect of waveguide, write pole and moving recording medium on the heated spot size is also investigated.