Download or read book Quantum Edge Transport in Topological Insulators written by Andrew J. Bestwick and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In the quantum Hall effect, electrons circulate in one direction around the edge of a 2D sample. The robustness of these states is protected by the topology of the band structure and scattering is only possible if thermally-activated 2D conduction provides a path across the bulk. However, the environmental conditions required for the effect (large magnetic fields and, usually, low temperatures) make it unsuitable for most practical applications. This dissertation discusses the implementation of two similar topological transport phenomena, in the absence of magnetic fields, using the class of materials known as topological insulators. First, it reports on investigations into the quantum spin Hall effect, a time-reversal-symmetric state with counterpropagating, spin-polarized edge channels. Mean free paths in this case are limited to only a few micrometers due to a scattering mechanism under investigation. Second, it reports on recent results on the quantum anomalous Hall effect demonstrating part-per-10,000 conductance quantization, arising from nearly perfect transport through one-way edge channels, in magnetically-doped thin films of 3D topological insulators. It shows that dissipation only occurs due to thermally-activated states that can be nearly eliminated via an unexpected magnetocaloric effect.

Download or read book Topological Insulators written by Gregory Tkachov and published by CRC Press. This book was released on 2015-10-14 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is the result of dynamic developments that have occurred in condensed matter physics after the recent discovery of a new class of electronic materials: topological insulators. A topological insulator is a material that behaves as a band insulator in its interior, while acting as a metallic conductor at its surface. The surface current car

Download or read book Topological Insulators written by C. Brüne and published by Elsevier Inc. Chapters. This book was released on 2013-11-23 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: This chapter will focus on the experimental properties of the quantum spin Hall effect in HgTe quantum well structures. HgTe quantum wells above a critical thickness are 2-dimensional topological insulators. The most prominent signature of the non-trivial topology in these systems is the occurrence of the quantum spin Hall effect when the Fermi energy is located inside the bulk band gap. We will present the main experimental results we obtained for transport in the quantum spin Hall regime and discuss how they confirm the prediction of the quantum spin Hall effect as a helical edge state system consisting of two counterpropagating oppositely spin polarized edge states.

Download or read book Emergent Transport Properties of Magnetic Topological Insulator Heterostructures written by Kenji Yasuda and published by Springer Nature. This book was released on 2020-09-07 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reveals unique transport phenomena and functionalities in topological insulators coupled with magnetism and superconductivity. Topological insulators are a recently discovered class of materials that possess a spin-momentum-locked surface state. Their exotic spin texture makes them an exciting platform for investigating emergent phenomena, especially when coupled with magnetism or superconductivity. Focusing on the strong correlation between electricity and magnetism in magnetic topological insulators, the author presents original findings on current-direction-dependent nonreciprocal resistance, current-induced magnetization reversal and chiral edge conduction at the domain wall. In addition, he demonstrates how the coupling between superconductivity and topological surface state leads to substantial nonreciprocal resistance. The author also elucidates the origins of these phenomena and deepens readers’ understanding of the topologically nontrivial electronic state. The book includes several works which are published in top journals and were selected for the President’s Award by the University of Tokyo and for the Ikushi Prize, awarded to distinguished Ph.D. students in Japan.

Download or read book Quantum Transport in 2 and 3 Dimensional Topological Insulators written by Di Xiao and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Topological insulators are materials that are insulating in the bulk but that conduct via topologically protected states on the boundary. The concept of topology in condensed matter physics was first introduced to explain the integer quantum Hall (IQH) effect. The perfect quantization of these topologically protected edge states, insensitive to sample geometry and disorder, stimulated an extensive search for many exciting new topological materials. One of the milestones along the journey was the theoretical prediction and experimental discovery of Z2 topological insulators.The first class of Z2 topological insulators discovered was the 2-dimensional topological insulator (2D TI), also known as the quantum spin Hall (QSH) insulator. The 2D TI can be viewed as a variation of the IQH system but with time-reversal-symmetry (TRS). The topological invariant for a 2D TI is the Z2 number, defined by its nontrivial band structure instead of the Chern number in the IQH case. Generalizing this idea to 3 dimensions led to the discovery of the 3D TI with four Z2 invariants. Both the 2D and 3D TIs are of interest as model platforms for testing theoretical problems of fundamental interest. For instance, they allow us to realize artificial condensed matter analogs of fundamental particles such as Majorana fermions and axions that have yet to be observed in nature. They are also of interest for potential technological applications, principally spintronics and quantum computing.This dissertation focuses on the synthesis, characterization, and transport properties of both 2D and 3D TIs. We first discuss the 2D TI candidate material system, type II InAs/GaSb quantum wells, which exhibits a rich topological phase diagram that can be tuned by several parameters such as sample geometry or electrostatic gating. By changing the thicknesses of relevant layers, we are able to enter a new insulating regime where unexpected high-density quantum oscillations are observed. We elucidate this phenomenon through theoretical calculation and through control experiments. The seemingly controversial coexistence of high density states and the insulating regime can be explained by the effect of the attractive Coulomb interaction, which was not considered in earlier theories.The second topic we address is quantum transport in 3D TI systems. Breaking the TRS of the 3D TI surface states leads to many exotic phenomena, including the quantum anomalous Hall (QAH) effect and the axion insulator state. By constructing a sandwich heterostructure that has different magnetic coercive fields in the top and bottom magnetic layers, while keeping the center layer free from magnetic impurities, both the QAH and the axion insulator state can be observed in low-temperature transport measurements, when the magnetization alignment of the top and bottom layers is parallel and antiparallel, respectively. We also discuss the scaling behavior of the topological quantum phase transition between these two states.

Download or read book Topological Insulators written by Frank Ortmann and published by John Wiley & Sons. This book was released on 2015-04-07 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are only few discoveries and new technologies in physical sciences that have the potential to dramatically alter and revolutionize our electronic world. Topological insulators are one of them. The present book for the first time provides a full overview and in-depth knowledge about this hot topic in materials science and condensed matter physics. Techniques such as angle-resolved photoemission spectrometry (ARPES), advanced solid-state Nuclear Magnetic Resonance (NMR) or scanning-tunnel microscopy (STM) together with key principles of topological insulators such as spin-locked electronic states, the Dirac point, quantum Hall effects and Majorana fermions are illuminated in individual chapters and are described in a clear and logical form. Written by an international team of experts, many of them directly involved in the very first discovery of topological insulators, the book provides the readers with the knowledge they need to understand the electronic behavior of these unique materials. Being more than a reference work, this book is essential for newcomers and advanced researchers working in the field of topological insulators.

Download or read book Studies on Time reversal Invariant Topological Insulators written by Joseph Maciejko and published by Stanford University. This book was released on 2011 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation brings together a number of topics in the theory of time-reversal invariant topological insulators. The first four chapters are devoted to the transport properties of the two-dimensional (2D) quantum spin Hall state. We explain nonlocal transport measurements in mercury telluride (HgTe) quantum wells in terms of a Landauer-Büttiker theory of helical edge transport and confirm the discovery of the quantum spin Hall state in this material. We find that decoherence can lead to backscattering without breaking microscopic time-reversal symmetry. As an example of incoherent scattering, we study a Kondo impurity in an interacting helical edge liquid. A renormalization group analysis shows the existence of an impurity quantum phase transition governed by the Luttinger parameter of the edge liquid between a local helical Fermi liquid with T^6 scaling of the low-temperature conductance, and an insulating strongly correlated phase with fractionally charged emergent excitations. In the presence of a time-reversal symmetry breaking magnetic field, it is known that even coherent scattering can lead to backscattering. Through exact numerical diagonalization we find that nonmagnetic quenched disorder has a strong localizing effect on the edge transport if the disorder strength is comparable to the bulk gap. The predicted magnetoconductance agrees qualitatively with experiment. The last two chapters are devoted to 3D topological insulators. We propose a combined magnetooptical Kerr and Faraday rotation experiment as a universal measure of the Z_2 invariant. Finally, we propose a fractional generalization of 3D topological insulators in strongly correlated systems, characterized by ground state degeneracy on topologically nontrivial spatial 3-manifolds, a quantized fractional bulk magnetoelectric polarizability without time-reversal symmetry breaking, and a halved fractional quantum Hall effect on the surface.

Download or read book Topological Insulators and Topological Superconductors written by B. Andrei Bernevig and published by Princeton University Press. This book was released on 2013-04-07 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: This graduate-level textbook is the first pedagogical synthesis of the field of topological insulators and superconductors, one of the most exciting areas of research in condensed matter physics. Presenting the latest developments, while providing all the calculations necessary for a self-contained and complete description of the discipline, it is ideal for graduate students and researchers preparing to work in this area, and it will be an essential reference both within and outside the classroom. The book begins with simple concepts such as Berry phases, Dirac fermions, Hall conductance and its link to topology, and the Hofstadter problem of lattice electrons in a magnetic field. It moves on to explain topological phases of matter such as Chern insulators, two- and three-dimensional topological insulators, and Majorana p-wave wires. Additionally, the book covers zero modes on vortices in topological superconductors, time-reversal topological superconductors, and topological responses/field theory and topological indices. The book also analyzes recent topics in condensed matter theory and concludes by surveying active subfields of research such as insulators with point-group symmetries and the stability of topological semimetals. Problems at the end of each chapter offer opportunities to test knowledge and engage with frontier research issues. Topological Insulators and Topological Superconductors will provide graduate students and researchers with the physical understanding and mathematical tools needed to embark on research in this rapidly evolving field.

Download or read book Transport Studies of Mesoscopic and Magnetic Topological Insulators written by Abhinav Kandala and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Topological Insulators (TI) are a novel class of materials that are ideally insulating in the bulk, but have gapless, metallic states at the surface. These surface states have very exciting properties such as suppressed backscattering and spin-momentum locking, which are of great interest for research efforts towards dissipation-less electronics and spintronics. The popular thermo-electrics from the Bi chalcogenide family -- Bi2Se3 and Bi2Te3 -- have been experimentally demonstrated to be promising candidate TI materials, and form the chosen material system for this dissertation research. The first part of this dissertation research focuses on low temperature magneto-transport measurements of mesoscopic topological insulator devices (Chapter 3). The top-down patterning of epitaxial thin films of Bi2Se3 and Bi2Te3 (that are plagued with bulk conduction) is motivated, in part, by an effort to enhance the surface-to-volume ratio in mesoscopic channels. At cryogenic temperatures, transport measurements of these devices reveal periodic conductance fluctuations in straight channel devices, despite the lack of any explicit patterning of the TI film into a ring or a loop. A careful analysis of the surface morphology and comparison with the transport data then demonstrate that scattering off the edges of triangular plateaus at the surface leads to the creation of Aharonov-Bohm electronic orbits responsible for the periodicity. Another major focus of this dissertation work is on combining topological insulators with magnetism. This has been shown to open a gap in the surface states leading to possibilities of magnetic "gating" and the realization of dissipation-less transport at zero-field, amongst several other exotic quantum phenomena. In this dissertation, I present two different schemes for probing these effects in electrical transport devices -- interfacing with insulating ferromagnets (Chapter 4) and bulk magnetic doping (Chapter 5). In Chapter 4, I shall present the integration of GdN with Bi2Se3 thin films. Careful structural, magnetic and electrical characterization of the heterostructures is employed to confirm that the magnetic species is solely restricted to the surface, and that the ferromagnetic GdN layer to be insulating, ensuring current flow solely through the TI layer. We also devise a novel device geometry that enables direct comparison of the magneto-transport properties of TI films with and without proximate magnetism, all, in a single device. A comparative study of weak anti-localization suggested that the overlying GdN suppressed quantum interference in the top surface state. In our second generation hetero-structure devices, GdN is interfaced with low-carrier density, gate-tunable thin films of (Bi,Sb)2Te3 grown on SrTiO3 substrates. These devices enable us to map out the comparison of magneto-transport, as the chemical potential is tuned from the bulk conduction band into the bulk valence band.In a second approach to study the effects of magnetism on TI's, I shall present, in Chapter 5, our results from magnetic doping of (Bi,Sb)2Te3 thin films with Cr -- a system that was recently demonstrated to be a Quantum Anomalous Hall (QAH) insulator. In a Cr-rich regime, a highly insulating, high Curie temperature ferromagnetic phase is achieved. However, a careful, iterative process of tuning the composition of this complex alloy enabled access to the QAHE regime, with the observation of near dissipation-less transport and perfect Hall quantization at zero external field. Furthermore, we demonstrate a field tilt driven crossover between a quantum anomalous Hall phase and a gapless, ferromagnetic TI phase. This crossover manifests itself in an electrically tunable, giant anisotropic magneto-resistance effect that we employ as a quantitative probe of edge transport in this system.

Download or read book Quantum Transport in Topological Insulators written by Johannes Krotz and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book QUANTUM TRANSPORT IN TOPOLOGICAL MATERIALS written by Run Xiao and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation focuses on the synthesis, characterization, fabrication, and electrical transport measurements of topological materials, including magnetically doped topological insulators and Dirac semimetal Cd3As2. Bismuth-chalcogenide topological insulators have time-reversal-symmetry-protected surface states due to the strong spin-orbit coupling. Breaking the time-reversal symmetry by magnetic dopants can lead to fascinating exotic phenomena, such as the quantum anomalous Hall effect. On the other hand, Dirac semimetals host three-dimensional Dirac fermions and can be identified as a parent phase of other topological phases, such as Weyl semimetals. In this dissertation, quantum transport measurements are performed on thin films of topological materials to investigate and understand the unusual electronic states that host these topological phases. These studies can motivate and facilitate the development of potential applications of topological materials, especially in spintronics and quantum computing. The first topological material studied in this dissertation is a magnetically doped topological insulator system: Cr doped (Bi,Sb)2Te3 - (Bi,Sb)2Te3 - Cr doped (Bi,Sb)2Te3 sandwich heterostructure. By tuning the chemical and asymmetric potentials using dual gates, both the quantum anomalous hall effect, due to the topology in the momentum space, and the topological Hall effect, due to the topology in real space, can be observed in this heterostructure system. We also mapped out a phase diagram of the topological Hall and quantum anomalous Hall effects as a function of the chemical and asymmetry potentials, paving a way to understand and manipulate the chiral magnetic spin textures in real space. The second topological material is Dirac semimetal Cd3As2. We investigated the integer quantum Hall effect in Cd3As2 thin films under strong to moderate quantum confinement (thicknesses of 10 nm, 12 nm, and 15 nm). In all the films, we observed the integer quantum Hall effect in the spin-polarized lowest Landau level (filling factor [nu]=1) and at spin-degenerate higher index Landau levels with even filling factors ([nu]=2,4,6). We also observed the lifting of the Landau level spin degeneracy at v=3 with strong quantum confinement. A tight-binding calculation suggests that the enhanced g-factor due to the quantum confinement and corrections from nearby subbands can be the reason for the emergence of v=3 quantum Hall plateau. Last, we explored the introduction of the transition metal Mn into Cd3As2 thin films to break the time-reversal symmetry. Scanning transmission electron microscopy of these films shows a formation of an Mn-rich layer on top of a pure Cd3As2 layer using both uniform and delta doping methods. The low solubility of Mn in Cd3As2 can be the reason for the phase separation. The Mn-rich region shows out-of-plane magnetic anisotropy in superconducting quantum interference device magnetometry measurements. Moreover, the presence of the Mn surfactant lowers the carrier density in the Cd3As2 layer, and an incipient quantum Hall effect can be observed in low-temperature transport measurements.

Download or read book Topological Insulators written by Joel E. Moore and published by Elsevier Inc. Chapters. This book was released on 2013-11-23 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: The theory of the topological insulator phase that emerges via spin-orbit coupling in three-dimensional materials is introduced, stressing its relationship to earlier topological phases in two dimensions. An unusual surface state with an odd number of “Dirac points” appears as a consequence of bulk topological invariants of the band structure. A different theoretical approach is then presented, based on the Berry phase of Bloch electrons, in order to illustrate a deep connection to the orbital contribution to the magnetoelectric polarizability in all materials. The unique features of transport in the topological insulator surface state are reviewed with an emphasis on possible experiments. The final section discusses briefly connections to interacting phases including topological superconductors and some recent efforts to construct fractional topological insulators in three dimensions.

Download or read book Quantum Electronic Transport in Atomically Layered Topological Insulators written by Valla Fatemi and published by . This book was released on 2018 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: The merger of topology and symmetry established a new foundation for understanding the physics of condensed matter, beginning with the notion of topological insulators (TIs) for electronic systems. For the time-reversal invariant TIs, a key aspect is the "helical" mode at the boundary of the system - that is, the ID edge of a 2D topological insulator or the 2D surface of a 3D topological insulator. These helical modes represent the extreme limit of spin-orbit coupling in that the spin-degenercy has been completely lifted while preserving time-reversal symmetry. This property is crucial for proposals realizing exotic excitations like the Majorana bound state. In this thesis, I present a series of experiments investigating electronic transport through the boundary modes of 3D and 2D topological insulators, specifically Bi1.5 Sb0.5 Te1.7 Se1.3 and monolayer WTe 2 , respectively. For the case of ultra-thin WTe 2 , I also present experiments detailing investigations of the 2D bulk states, finding a semimetallic state for the trilayer and a superconducting phase for the monolayer, both of which are strongly tunable by the electric field effect. The discovery of 2D topological insulator and 2D superconductor phases within the same material, accessible by standard solid state elecrostatic gates, places WTe2 in a unique situation among both TIs and superconductors, potentially enabling gate-configurable topological devices within a homogenous material platform.

Download or read book Quantized Phenomena of Transport and Magneto Optics in Magnetic Topological Insulator Heterostructures written by Masataka Mogi and published by Springer Nature. This book was released on 2022-05-07 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents experimental studies on emergent transport and magneto-optical properties in three-dimensional topological insulators with two-dimensional Dirac fermions on their surfaces. Designing magnetic heterostructures utilizing a cutting-edge growth technique (molecular beam epitaxy) stabilizes and manifests new quantization phenomena, as confirmed by low-temperature electrical transport and time-domain terahertz magneto-optical measurements. Starting with a review of the theoretical background and recent experimental advances in topological insulators in terms of a novel magneto-electric coupling, the author subsequently explores their magnetic quantum properties and reveals topological phase transitions between quantum anomalous Hall insulator and trivial insulator phases; a new topological phase (the axion insulator); and a half-integer quantum Hall state associated with the quantum parity anomaly. Furthermore, the author shows how these quantum phases can be significantly stabilized via magnetic modulation doping and proximity coupling with a normal ferromagnetic insulator. These findings provide a basis for future technologies such as ultra-low energy consumption electronic devices and fault-tolerant topological quantum computers.

Download or read book Topological Insulators written by Inamuddin and published by Materials Research Forum LLC. This book was released on 2024-01-15 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: A topological insulator is an area that has yet to be fully explored and developed. The charge-induced bandgap fluctuation in the best-known bismuth-chalcogenide-based topological insulators is approximately 10MeV in magnitude. The major focus has shifted to the investigation of the presence of high-symmetry electronic bands as well as the utilization of easily produced materials. As the subject of topological insulators is still in the nascent stage, there is growing research and knowledge in the emerging field. This book is intended to provide the readers with an understanding of the needs and application of these materials. Keywords: Topological Insulators, Insulators, One-Dimensional Topological Insulators, Graphene, Magnetic Topological Insulator, Antiferromagnetic Phase, Ferromagnetic Phase, Topological Superconductor, Nonlinear Optical Behavior, Saturable Absorber, Quantum, Band Gap, Photonic Topological Insulators.

Download or read book A Short Course on Topological Insulators written by János K. Asbóth and published by Springer. This book was released on 2016-02-22 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological insulators. The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible. The present approach uses noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one-dimensional case (the Su-Schrieffer-Heeger model for polyacetylene) to two-dimensional time-reversal invariant topological insulators (the Bernevig-Hughes-Zhang model for HgTe). In each case the discussion of simple toy models is followed by the formulation of the general arguments regarding topological insulators. The only prerequisite for the reader is a working knowledge in quantum mechanics, the relevant solid state physics background is provided as part of this self-contained text, which is complemented by end-of-chapter problems.

Download or read book Topological Insulators written by Chaoxing Liu and published by Elsevier Inc. Chapters. This book was released on 2013-11-23 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the chapter, we review two proto-type models of topological insulators, namely the Bernevig-Hughes-Zhang model for HgTe quantum wells and the four band model for family of materials. Based on these two simple models, we discuss helical edge/surface states of topological insulators, as well as their exotic physical properties, including total angular momentum, spin and orbital textures, topological stability, and topological response of the surface states. Moreover, we summarize the basic principle to search for topological insulators from these two models and discuss the related topological materials.