Quantum spin hall effect in ivvi topological crystalline. Zhang is a professor of physics at stanford university in stanford, california. The search for topological states of matter that do not require magnetic fields for their observation led to the theoretical prediction in 2006 and experimental observation in 2007 of the socalled quantum spin hall effect in hgte quantum wells, a new topological state of quantum. Topological insulators tis and the quantum spin hall qsh effect attract significant interest for both fundamental and practical reasons.
Topological spin texture in a quantum anomalous hall. A threedimensional 3d topological insulator supports novel spin polarized 2d dirac fermions on its surface. Pdf a topological dirac insulator in a quantum spin hall. Pdf topological spin texture in quantum anomalous hall. A conductive topological insulator with large spin hall. An example of the quantum hall effect in a band theory is provided by a simple model of graphene in a periodic magnetic field introduced by haldane 34. The noninteracting models discussed in this section can. In this colloquium the theoretical foundation for topological insulators. The realization of the quantum spin hall effect in hgte quantum wells has led to the development of topological materials which, in combination with magnetism and superconductivity, are predicted to host chiral majorana fermions. The study of such trsbreaking systems is one of the most emerging frontiers in condensedmatter physics.
Experimentalists have observed the predicted halfinteger quantum hall effect using the topological insulator bisbtese2, which exhibits topological surface states at room temperature, with each. Quantum spin hall qsh insulators are topological state of matter driven by the spin orbit coupling, a singleparticle relativistic effect 9, 10. New topological insulators that demonstrate the quantum anomalous hall effect qahe are a cuttingedge research topic in condensed matter physics and materials science. It also provides a stepping stone to the 2d quantum spin hall insulator. Over a long period of exploration, the successful observation of quantized version of anomalous hall effect ahe in thin film of magneticallydoped topological insulator completed a quantum hall trio quantum hall effect qhe, quantum spin hall effect qshe, and quantum anomalous hall effect qahe. Topological insulators and the quantum spin hall effect. Mele department of physics and astronomy, university of pennsylvania, philadelphia, pennsylvania 19104, usa received 22 june 2005. This pair of helical hinge modes are localized on the hinges of the top and bottom surfaces of the afm ti multilayers. Quantum oscillations and hall anomaly of surface states in. To overcome the limitations imposed by the low spin orbit interaction in graphene, the quantum spin hall qsh phase was early on proposed by bernevig and zhang in intricate strain architecture promoted by strong spin orbit coupling. Recently, a new class of topological states has emerged, called quantum spin hall qsh states or topological insulators see physics today, january 2008, page 19. The quantum anomalous hall qah effect, also called chern insulating phase, is a twodimensional 2d topological state of quantum matter which exhibits a. Record surface state mobility and quantum hall effect in. Quantum spin hall effect and topological insulators for light.
Quantum spin hall effect majorana fermions magnetic monopole and dyon tme effect and axion. Unlike the conventional qsh effect, the hqsh effect survives the breaking of timereversal symmetry. The quantum hall state is the first, and so far the only example, of a topologically nontrivial state of matter, where the quantization of the hall conductance is protected by a topological invariant. Tomonagaluttinger liquid in the edge channels of a. However, the similarity between chiral spin states and quantum hall states allows one to use the theory of topological order to describe different quantum hall states. Bliokh1,2 and franco nori1,3 1 center for emergent matter science, riken, wakoshi. Quantum spin hall effect and topological insulators for light konstantin y.
We show that the quantum spin hall effect, a state of matter with topological properties distinct from conventional insulators, can be realized in hgtecdte semiconductor quantum wells. These are characterized by a nonzero topological spin chern number, and manifest themselves as. Topological insulators and the quantum spin hall effect i. The integer and fractional quantum hall effects were the first topological. Because the electronic structures of sn allotropes are sensitive to lattice strain, e. The anomalous hall effect is a fundamental transport process in solids arising from the spin orbit coupling. Pdf quantum spin hall effect in 2d topological insulators.
We present a theoretical realization of quantum spin and quantum valley hall effects in silicene. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Pdf the quantum spin hall effect and topological insulators. In particular, efforts to achieve thin ti samples with dominant surface transport have always led to increased defects and degraded mobilities, thus making it difficult to probe the quantum regime of the topological surface states. We show that the quantum spin hall qsh effect, a state of matter with topological properties distinct from those of conventional insulators, can be realized in mercury telluridecadmium telluride semiconductor quantum wells. Quantum spin hall systems and topological insulators iopscience. Spin orbit torque switching using the spin hall effect in heavy metals and topological insulators has a great potential for ultralow power magnetoresistive randomaccess memory. Pdf the original motivation of great interest to topological insulators was the hope to observe the. Therefore if a material is in the topological insulator state they.
Quantum spin hall effect and topological phase transition. This phase transition from a two dimensional topological insulator to a trivial insulating state is accompanied by a quenching of the quantum spin. Therefore, it is important to find new materials with large topological band gap and high thermal stability for. So far, the qahe has been observed only in crdoped bi,sb2te3 at extremely low temperature. Note that the gapless surface states of topological insulators differ from those in the quantum hall effect. Here we investigate the spin degree of freedom of a qah insulator and uncover the fundamental phenomenon that the edge. Graphenes exceptionally weak spin orbit couplingstemming from carbons low massposes the primary obstacle. Z2 topological order and the quantum spin hall effect.
On the theoretical front, it was understood that intrinsic ahe is related to. Topological insulators quantum spin hall systems are insulating in the bulk but have gapless edgesurface states, which remain. An atomic layer of tin in a buckled honeycomb lattice, termed stanene, is a promising largegap twodimensional topological insulator for realizing roomtemperature quantum spin hall effect and therefore has drawn tremendous interest in recent years. The quantum spin hall effect is a unique phase of matter in which the bulk of the material is an insulator, but topological quantum states exist at. The original motivation of great interest to topological insulators was the hope to observe the quantum spin hall effect. The doping, however, introduces inhomogeneity, reducing the temperature at which the effect occurs. Pdf quantum spin hall effect and topological insulators. Half quantum spin hall effect on the surface of weak. Topological insulator is a triumph of topological order in condensed matter physics. Discovery of the integer and fractional quantum hall effects in the 1980s opens a new window to explore the mystery of condensed matters. Edge states and integer quantum hall effect in topological. Just like chiral spin states, different quantum hall states all have the same symmetry and are outside the landau symmetrybreaking description. Quantum spin hall insulator with a large bandgap, dirac.
Realization of the quantum spin hall effect in graphene devices has remained an outstanding challenge dating back to the inception of the field of topological insulators. Valley polarized quantum hall effect and topological insulator phase transitions in silicene. Quantum spin hall insulator state in hgte quantum wells. The topological kitaev models and the ti insulators including the integer quantum hall effect,, show that disorder can play a useful role in stabilizing topologically ordered states and could play a role in guiding the experimental discovery of topological quantum spin liquids.
By varying the thickness of the quantum well, the electronic state changes from a normal to an inverted type at a. Quantum spin hall effect and topological insulators nanotec. Valley polarized quantum hall effect and topological. Evidence for a quantum spin hall phase in graphene. We propose a new class of semiconductor systems based on multilayer brokengap quantum wells, in which the qshi gap reaches 60 mev and remains. For a video introduction of topological insulators, see this url. Introduction topological band theory and topological insulators ii. Material defects remain as the main bottleneck to the progress of topological insulators tis. This model is important because it provides a simple 2 band description of the quantum hall effect. The quantum spin hall effect and topological insulators xiaoliang qi and shoucheng zhang in topological insulators, spin orbit coupling and timereversal symmetry combine to form a novel state of matter predicted to have exotic physical properties.
Quantum anomalous hall effect in intrinsic magnetic. We present a topological description of the quantum spin hall effect qshe in a twodimensional electron system on a honeycomb lattice with both intrinsic and rashba spin orbit couplings. We show that combination of an electric field and intrinsic spin orbit interaction leads to quantum phase transitions at the charge neutrality point. Such a nontrivial state exhibiting or not exhibiting a quantum spin hall effect is called a topological insulator, which is an example of symmetryprotected topological order protected by charge conservation symmetry and time reversal symmetry. We experimentally and theoretically study artificially enhanced spin orbit. In this work, we predict a hinged quantum spin hall hqsh effect featured by a pair of helical hinge modes in antiferromagnetic afm topological insulator ti multilayers. The quantum spin hall effect and topological insulators. Topological insulators topological insulator surface states.
Quantum spin hall effect in 2d topological insulators. Quantum anomalous hall effect and related topological. Pdf quantum spin hall effect and topological insulators for light. We show that freespace light has intrinsic quantum spinhall effect qshe properties. Quantum spinvalley hall effect and topological insulator. Quantized anomalous hall effect in magnetic topological. Magnetic topological insulators and quantum anomalous hall.
Observation of topological surface state quantum hall. Quantum spin hall insulators are twodimensional materials that host conducting helical electron states strictly confined to the onedimensional boundaries. In a quantum anomalous hall insulator, spontaneous magnetic moments and spin orbit coupling combine to give rise to a topologically nontrivial electronic structure, leading to the quantized hall effect without an external magnetic field. Therefore if a material is in the topological insulator state they frequently call it the quantum spin hall state. When the magnetic order is introduced into topological insulators tis, the timereversal symmetry trs is broken, and the nontrivial topological surface is driven into a new massive dirac fermions state. When the thickness of the quantum well is varied, the electronic state changes from a normal to an inverted type at a critical. Here, by utilizing a novel buffer layer scheme composed of. In topological insulators, spinorbit coupling and timereversal symmetry combine to form a novel state of matter predicted to have exotic physical properties. This state is predicted to be associated with high carrier mobility. Therefore, the surface state of a weak topological insulator with translation symmetry breaking on the surface has a half quantum spin hall effect, in the same way that the surface state of a strong topological insulator with timereversal symmetry breaking on the surface has a half quantum hall effect. Topologically distinct from all other known states of matter, including qh states, qsh states have been theoretically predicted and experimentally observed in mercury telluride quantum wells, 2,3 2. Topological insulators and quantum anomalous hall effect. The integer and fractional quantum hall effects were the first topological states to be discovered in.
Quantum hall effect an overview sciencedirect topics. Quantum spin hall effect and topological insulators. The quantum spin hall qsh insulators 46 have a similar, but distinct, nontrivial topological property. In the threedimensional 3d and twodimensional 2d tis the bulk insulating states are accompanied by metallic helical diraclike massless electronic states on the surface edges of the crystal. In topological insulators, spin orbit coupling and timereversal symmetry combine to form a novel state of matter predicted to have exotic physical properties. The search for room temperature quantum spin hall insulators qshis based on widely available materials and a controlled manufacturing process is one of the major challenges of todays topological physics. Quantum spin hall effect time reversal symmetry and edge states experiment.
77 1189 394 1465 176 1117 243 470 28 15 1039 1063 657 809 1217 1207 1319 832 859 824 691 863 154 1197 1498 1030 356 712 669 698 520 1554 375 652 365 1262 905 864 168 1042 1096 1236 1477 814