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 Electronic Transport of a 2D Quantum Material WTe2 written by Wenjin Zhao and published by . This book was released on 2020 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum materials, such as superconductors, topological insulators, magnets, and Weyl semimetals, are materials whose properties cannot be explained without quantum mechanics. Strong correlation and band topology play very important roles in quantum materials. The study of two-dimensional (2D) quantum materials was triggered by the discovery of graphene, the first atomically thin crystal wherein electrons are confined in a single 2D sheet. In this regime, critical material parameters such as carrier density, electron correlation strength and topology can be modified by electrostatic gate, screening effect and magnetic field, respectively. Moreover, the stacking of different 2D quantum materials enables creation of novel structures which can host new electronic phenomena and realize new device functionalities. All of these make 2D quantum materials a perfect platform to study the physics of strong correlation, magnetism, and topology. This thesis focuses on electronic properties of a 2D quantum material WTe2. In the first part, I will discuss the discovery of the first ferroelectric metal in few-layer WTe2. As WTe2 is thinned down to trilayer and bilayer, it exhibits coexistence of ferroelectric and metallic phases. Then, I will discuss the quantum spin Hall (QSH) edge state of a monolayer WTe2 in three aspects. The spin axis is first established by study of the anisotropy of conductance in an external magnetic field. Then I will show the magnetic proximity effect between the QSH edge and a 2D magnet CrI3. Finally, I will summarize the experiment of spin current injection into the QSH edge.

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 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 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 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 Ke He and published by Elsevier Inc. Chapters. This book was released on 2013-11-23 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: Material is a key to the experimental observation of novel quantum phenomena predicted in topological insulators. In this chapter, we review the recent theoretic and experimental efforts devoted to improving the existing topological insulator materials and exploring new topological insulators. The emphasis is on growth and engineering of the properties of topological insulator thin films by molecular beam epitaxy for realization of various quantum effects.

Download or read book An Introduction to Quantum Transport in Semiconductors written by David K. Ferry and published by CRC Press. This book was released on 2017-12-14 with total page 538 pages. Available in PDF, EPUB and Kindle. Book excerpt: Throughout their college career, most engineering students have done problems and studies that are basically situated in the classical world. Some may have taken quantum mechanics as their chosen field of study. This book moves beyond the basics to highlight the full quantum mechanical nature of the transport of carriers through nanoelectronic structures. The book is unique in that addresses quantum transport only in the materials that are of interest to microelectronics—semiconductors, with their variable densities and effective masses. The author develops Green’s functions starting from equilibrium Green’s functions and going through modern time-dependent approaches to non-equilibrium Green’s functions, introduces relativistic bands for graphene and topological insulators and discusses the quantum transport changes that these bands induce, and discusses applications such as weak localization and phase breaking processes, resonant tunneling diodes, single-electron tunneling, and entanglement. Furthermore, he also explains modern ensemble Monte Carlo approaches to simulation of various approaches to quantum transport and the hydrodynamic approaches to quantum transport. All in all, the book describes all approaches to quantum transport in semiconductors, thus becoming an essential textbook for advanced graduate students in electrical engineering or physics.

Download or read book Topological Insulators written by and published by Elsevier. This book was released on 2013-11-23 with total page 349 pages. Available in PDF, EPUB and Kindle. Book excerpt: Topological Insulators, volume six in the Contemporary Concepts of Condensed Matter Series, describes the recent revolution in condensed matter physics that occurred in our understanding of crystalline solids. The book chronicles the work done worldwide that led to these discoveries and provides the reader with a comprehensive overview of the field. Starting in 2004, theorists began to explore the effect of topology on the physics of band insulators, a field previously considered well understood. However, the inclusion of topology brings key new elements into this old field. Whereas it was thought that all band insulators are essentially equivalent, the new theory predicts two distinct classes of band insulators in two spatial dimensions and 16 classes in three dimensions. These "topological" insulators exhibit a host of unusual physical properties, including topologically protected gapless surface states and exotic electromagnetic response, previously thought impossible in such systems. Within a short time, this new state of quantum matter, topological insulators, has been discovered experimentally both in 2D thin film structures and in 3D crystals and alloys. It appears that topological insulators are quite common in nature, and there are dozens of confirmed substances that exhibit this behavior. Theoretical and experimental studies of these materials are ongoing with the goal of attaining the fundamental understanding and exploiting them in future practical applications. Usable as a textbook for graduate students and as a reference resource for professionals Includes the most recent discoveries and visions for future technological applications All authors are prominent in the field

Download or read book Electronic Transport in Tunnel Junctions of Quantum Spin Hall Effect Topological Insulators written by Pietro Sternativo 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 Topological Insulators written by Vadim Nemytov and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "In this thesis we investigate quantum transport properties of topological insulator (TI) Bi2 Se3 from atomistic point of view. TI is a material having an energy gap in its bulk but supporting gapless helical states on its boundary. The helical states have Dirac-like linear energy dispersion continuously crossing the bulk band gap with a spin texture in which the electron spin is locked perpendicular to the electron momentum. The peculiar electronic structure of TI material Bi2 Se3 is due to a strong spin-orbit interaction and is protected by the time reversal symmetry. The thesis consists of two main parts. The first reviews the theory of TI and the second presents our atomistic calculations of electron transport in the Bi2 Se3 material. In the theoretical review of the physics of TI, I follow the literature and attempt to present it in a reasonably accessible manner. The theory of TI is explained in terms of well known physical phenomena including classical and quantum Hall effects, spin-orbit coupling, spin current, and spin-Hall effect. The concept of Berry's phase is then introduced to link with the formal conventionalclassification of TI by the topological Z2 invariants. The entire discussion is within the well known Bloch band theory. In the second part of this thesis, numerical studies of transport properties of Bi2 Se3 are presented. After a brief discussion of the relevant quantum transport theory and the tight binding atomistic model, we present our calculated quantum transport results of Bi2 Se3 films having a trench in the middle. Such a large defect, if on normal conductors, would cause significant back scattering of the carriers. Here, by topological protection of the helical states, back scattering is forbidden due to the spin-momentum locking. Nevertheless, large trenches in the film may cause the helical states on the surface to mix inside the trench, thereby affecting the transmission." --

Download or read book Topological Insulators written by Jeroen B. Oostinga and published by Elsevier Inc. Chapters. This book was released on 2013-11-23 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: The discovery of topological insulators as a new state of matter has generated immense interest in this new class of materials. Three-dimensional (3D) topological insulators are characterized by the presence of an odd number of families of Dirac fermions—ideally one- at each of their surfaces. Angle-resolved photoemission experiments have demonstrated the presence of the expected Dirac fermions, but it is clear that to explore the electronic properties of these systems, transport measurements in many different device geometries are called for, just as it has been the case for Dirac fermions in graphene. In this chapter we review the status of transport studies through 3D topological insulators as of early summer 2012, after that a first generation of experiments has been performed. The results provide many different indications of the presence of surface fermions, as well as evidence of their Dirac nature. However, no textbook “manifestation” of surface Dirac fermions has been reported so far in these materials. Indeed, experiments also show that investigations are severely hampered by the material quality in most cases, because of the effect of high conductivity in the bulk, of low carrier mobility, of technical difficulties hampering device fabrication, and other reasons. In this chapter, we attempt to give a balanced overview of the work done during this first period and of the results obtained, stressing the implications and the limits of many of the observations that have been reported in the literature.

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 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 Quantum Transport Properties in Tungsten Ditelluride Based Devices written by Xurui Zhang and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The success of mechanical exfoliation on graphene has paved a new field of research in two-dimensional (2D) materials. As one of the transition metal dichalcogenides (TMDCs), tungsten ditelluride (WTe2) has attracted a mass of interests since a novel non-saturating positive magnetoresistance was discovered in 2014. A lot of researches in this material have been published, such as band structure studies with angle-resolved photoelectron spectroscopy (ARPES), quantum oscillations in transport measurements, superconductivity in WTe2 etc. It is worth mentioning that the topological properties of WTe2 have been verified in both bulk (type-II Weyl semi-metal) and in monolayer (2D topological insulator) forms. The topological properties make WTe2 a potential candidate for hosting Majorana bound state, which is theoretically predicted to arise from the proximity effect between a s-wave superconductor and the surface states of a topological insulator (TI). This dissertation will present quantum transport studies in multi-layer WTe2, which acts as an intermediate between the bulk and monolayer limits. Our goal is to explore the transport properties in WTe2 itself, and investigate its interaction with other quantum materials, especially superconductors. A series of different types of devices based on multi-layer WTe2, including Hall bars, FET-like devices and Josephson junctions, have been fabricated and measured in the magnetic fields up to 12 T at low temperatures down to 20 mK. In order to improve the performance of the devices, the hexagonal boron nitride (hBN) flakes are used to build sandwiched structures for thin WTe2 flakes. The main results are presented as follows. First, thickness-dependent quantum transport measurements suggest that the novel "turn-on" behavior in WTe2 take the origin of the Kohler's rule in Fermi liquid state. The "turn-on" behavior accompanied by the large magnetoresistance (MR) will be effectively suppressed by the loss of perfect carrier compensation. Strikingly, however, the trend of non-saturation is unaffected at all which indicates the possibility of other origins of the non-saturating MR. In addition, the angle-dependent MR measurements reveal that the electronic 3D nature of multi-layer WTe2 and the Fermi surface anisotropy depends on the sample thickness. Second, we observe an obvious crossover between weak anti-localization (WAL) and weak localization (WL) in an disordered ultrathin WTe2 flake. The mechanism of the crossover shows coexistence and competition among several characteristic lengths, including the dephasing length, the spin-flip length, and the mean free path. Furthermore, the interplay of quantum interference and electron-electron interaction is also observed. Third, an unconventional quasi-3D quantum Hall effect (QHE) is observed in a high quality flake with much lower carrier density and higher mobility than ordinary WTe2. The quasi-3D QHE act as a collection of several weakly-coupled 2D QHE layers, which might be resulted from a dimerization or tetramization effect. Fourth, in the Ta-WTe2-Ta Josephson junctions, supercurrent state is successfully induced into the multi-layer WTe2 by proximity effect. We observe the fast mode superconducting quantum interference pattern, which indicates the presence of edge supercurrent resulted from the intrinsic edge states of WTe2. In addition, the multiple frequencies observed in the interference pattern might be from the terrace structure along the sample edges. Finally, the presence of the multi-dips in differential resistance in the Josephson junctions with incomplete superconducting state marks the multiple Andreev reflections in WTe2, which might be due to the multiple channels formed along the Josephson junction length. Furthermore, the related experimental procedures, improvements and different data processing methods have also been presented in the main text and appendixes.

Download or read book Topological Insulators written by Frank Ortmann and published by John Wiley & Sons. This book was released on 2015-04-08 with total page 432 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 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.