Quantum Anomalous Hall Effect in Magnetic Topological Insulators PDF Download
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Languages : en
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The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Here, we give a theoretical introduction to the quantum anomalous Hall (QAH) effect based on magnetic topological insulators in two-dimensions (2D) and three-dimensions (3D). In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state has been predicted to exist on the magnetic domain walls. We present the phase diagram in thin films of a magnetic topological insulator and review the basic mechanism of ferromagnetic order in magnetically doped topological insulators. We also review the recent experimental observation of the QAH effect. Furthermore, we discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, the theory of the plateau transition, and the thickness dependence in the QAH effect.
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Languages : en
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Book Description
The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Here, we give a theoretical introduction to the quantum anomalous Hall (QAH) effect based on magnetic topological insulators in two-dimensions (2D) and three-dimensions (3D). In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state has been predicted to exist on the magnetic domain walls. We present the phase diagram in thin films of a magnetic topological insulator and review the basic mechanism of ferromagnetic order in magnetically doped topological insulators. We also review the recent experimental observation of the QAH effect. Furthermore, we discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, the theory of the plateau transition, and the thickness dependence in the QAH effect.
Author: Xufeng Kou
Publisher:
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Languages : en
Pages : 222
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The engineering of topological surface states is a key to realize applicable devices based on topological insulators (TIs). Among various proposals, introducing magnetic impurities into TIs has been proven to be an effective way to open a surface gap and integrate additional ferromagnetism with the original topological order. In this Dissertation, we study both the intrinsic electrical and magnetic properties of the magnetic TI thin films grown by molecular beam epitaxy. By doping transition element Cr into the host tetradymite-type V-VI semiconductors, we achieve robust ferromagnetic order with a strong perpendicular magnetic anisotropy. With additional top-gating capability, we realize the electric-field-controlled ferromagnetism in the magnetic TI systems, and demonstrate such magneto-electric effects can be effectively manipulated, depending on the interplays between the band topology, magnetic exchange coupling, and structural engineering. Most significantly, we report the observation of quantum anomalous Hall effect (QAHE) in the Cr-doped (BiSb)2Te3 samples where dissipationless chiral edge conduction is realized in the macroscopic millimeter-size devices without the presence of any external magnetic field, and the stability of the quantized Hall conductance of e2/h is well-maintained as the film thickness varies across the 2D hybridization limit. With additional quantum confinement, we discover the metal-to-insulator switching between two opposite QAHE states, and reveal the universal QAHE phase diagram in the thin magnetic TI samples. In addition to the uniform magnetic TIs, we further investigate the TI/Cr-doped TI bilayer structures prepared by the modulation-doped growth method. By controlling the magnetic interaction profile, we observe the Dirac hole-mediated ferromagnetism and develop an effective way to manipulate its strength. Besides, the giant spin-orbit torque in such magnetic TI-based heterostructures enables us to demonstrate the current-induced magnetization switching with the critical current density much lower than other heavy metal/magnet systems. Our work on the magnetic TIs and their heterostructures thus unfolds new avenues for novel multifunctional nano-electronics and non-volatile spintronic applications.
Author: An Zhao
Publisher: Open Dissertation Press
ISBN: 9781361341209
Category :
Languages : en
Pages :
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This dissertation, "Theoretical Study of Magnetic Topological Insulators" by An, Zhao, 赵安, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: In recent years, the discovery of topological insulators brought a topological classification of materials and opened a new field in condensed matter physics. Due to the nontrivial topological properties, the topological insulators have insulating bulk and metallic edge/surface relating to some exotic physics such as quantum anomalous Hall effect, quantum spin Hall effect, and magneto-electric effect. Followed realizations of the Z2 topological insulators in two and three dimensions, the quantum anomalous Hall effect was realized in the magnetic-doped topological insulators very recently, which attracts intensive interest. In this thesis, the magnetic topological insulators as a consequence of time-reversal symmetry breaking in the Z2 topological insulators in two or three dimensions are studied. As an introduction, a review of the topological insulators including some relevant theories is given. The approaches involved in this study are also presented. The results can be summarized in two parts. First, the quantum anomalous Hall effect can be found on the two-dimensional decorated lattice with spin-orbit coupling and electron-electron interaction. Without interaction, this model exhibits the quantum spin Hall effect and has at bands in the middle of the spectra. A at-band ferrimagnetism which breaks the time-reversal symmetry and a charge-density wave can be induced by the electron-electron interaction. Altogether they can modulate the Chern number of the system and give rise to the quantum anomalous Hall effect. In the second part, the realization of the quantum anomalous Hall effect in magnetic-doped topological insulator thin films is investigated. With an effective Hamiltonian of the surface states of a topological insulator thin _lm, the condition of the quantum anomalous Hall effect and the behavior of the longitudinal and Hall conductivity is given, which agrees with the experimental results. The effects of the structural inversion asymmetry potential and the particle-hole symmetry breaking term are studied. With a thin _lm model of the three-dimensional topological insulator, it is shown that the lateral surface states account for the non-quantized value of the Hall conductance and the nonzero longitudinal conductance. The quantized Hall conductance restores when the lateral surface state electrons are thoroughly localized by disorder. The quantum anomalous Hall phase in magnetic topological insulator thin film in the present of disorder is also studied. The disorder will shrink the regime of the quantum anomalous Hall effect in a thick film and becomes an obstacle to the realization of the quantum anomalous Hall effect. DOI: 10.5353/th_b5194784 Subjects: Condensed matter
Author: Sadamichi Maekawa
Publisher: Oxford University Press
ISBN: 0198787073
Category : Science
Languages : en
Pages : 541
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Book Description
In a new branch of physics and technology, called spin-electronics or spintronics, the flow of electrical charge (usual current) as well as the flow of electron spin, the so-called "spin current", are manipulated and controlled together. This book is intended to provide an introduction and guide to the new physics and applications of spin current.
Author: Inamuddin
Publisher: Materials Research Forum LLC
ISBN: 1644902850
Category : Technology & Engineering
Languages : en
Pages : 195
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Book Description
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.
Author: Ruoxi Zhang
Publisher:
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Languages : en
Pages : 0
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Topological materials exhibit unique properties that make them robust against local defects and perturbations. These properties stem from the distinctive band structure compared to conventional materials, which are characterized by different topological invariants. In this thesis, we study two phenomena that arise in epitaxial topological insulator (TIs) films/heterostructures. The first phenomenon is the quantum anomalous Hall (QAH) effect. The QAH effect requires no external magnetic field and possesses non-dissipative chiral edge states that are resistant to local disorders. The second phenomenon is the topological superconducting (TSC) states. The TSC state hosts quasiparticle excitations, including Majorana zero modes (MZMs) and chiral Majorana edge modes (CMEMs). These excitations have potential applications in fault-tolerant topological quantum computations. The first experimental observation of the QAH effect was realized in molecular beam epitaxy (MBE)-grown magnetically doped TI thin films, which offer the advantages of scalability and reproducibility. However, the introduction of magnetic dopants also leads to higher disorder density in TI thin films. To overcome this limitation, we employed MBE-grown magnetically doped TI/TI/magnetically doped TI sandwich heterostructures to separate the magnetic dopants from the TI bulk. By employing this method, we successfully realized high Chern number QAH states, Chern domain walls, and hundred-nanometer-thick QAH samples. These results reveal new phases of matter and the underlying physics of the QAH phase transition induced by interlayer coupling. The second half of the thesis describes our effort in the TSC state in QAH insulators and TIs with induced superconductivity. The first project in this effort focuses on the search for CMEMs, which are predicted to emerge in QAH/superconductor hybrid structures. We examined a prior transport experiment that claimed the realization of CMEMs by measuring the two-terminal resistance. We improved the experimental design by fabricating Josephson junction and tunneling junction devices based on Bi2Te3 and (Bi,Sb)2Te3, and obtained transport results that suggest the dominance of Dirac surface states in vortex generation in the junction area.
Author: Kenji Yasuda
Publisher: Springer Nature
ISBN: 981157183X
Category : Computers
Languages : en
Pages : 109
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Book Description
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.
Author: Supriyo Datta
Publisher: Cambridge University Press
ISBN: 1139643010
Category : Science
Languages : en
Pages : 398
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Book Description
Advances in semiconductor technology have made possible the fabrication of structures whose dimensions are much smaller than the mean free path of an electron. This book gives a thorough account of the theory of electronic transport in such mesoscopic systems. After an initial chapter covering fundamental concepts, the transmission function formalism is presented, and used to describe three key topics in mesoscopic physics: the quantum Hall effect; localisation; and double-barrier tunnelling. Other sections include a discussion of optical analogies to mesoscopic phenomena, and the book concludes with a description of the non-equilibrium Green's function formalism and its relation to the transmission formalism. Complete with problems and solutions, the book will be of great interest to graduate students of mesoscopic physics and nanoelectronic device engineering, as well as to established researchers in these fields.
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Languages : en
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After decades of searching for the dissipationless transport in the absence of any external magnetic field, quantum anomalous Hall effect (QAHE) was recently achieved in magnetic topological insulator films. However, the universal phase diagram of QAHE and its relation with quantum Hall effect (QHE) remain to be investigated. Here, we report the experimental observation of the giant longitudinal resistance peak and zero Hall conductance plateau at the coercive field in the six quintuple-layer (Cr0.12Bi0.26Sb0.62)2Te3 film, and demonstrate the metal-to-insulator switching between two opposite QAHE plateau states up to 0.3 K. Moreover, the universal QAHE phase diagram is confirmed through the angle-dependent measurements. Our results address that the quantum phase transitions in both QAHE and QHE regimes are in the same universality class, yet the microscopic details are different. Additionally, the realization of the QAHE insulating state unveils new ways to explore quantum phase-related physics and applications.
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Languages : en
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The topological magnetoelectric effect in a three-dimensional topological insulator is a novel phenomenon, where an electric field induces a magnetic field in the same direction, with a universal coefficient of proportionality quantized in units of $e2/2h$. Here in this paper, we propose that the topological magnetoelectric effect can be realized in the zero-plateau quantum anomalous Hall state of magnetic topological insulators or a ferromagnet-topological insulator heterostructure. The finite-size effect is also studied numerically, where the magnetoelectric coefficient is shown to converge to a quantized value when the thickness of the topological insulator film increases. We further propose a device setup to eliminate nontopological contributions from the side surface.
