Voltage drop is measured to see whether the conductance becomes zero or not. Quantum spin hall qsh insulators have gapless topological edge states inside the bulk band gap, which can serve as dissipationless spin current channels. Magnetic topological insulators and quantum anomalous hall. The first theory of a qhe without a magnetic field was proposed in 1988. The story of the topological insulator began with the discovery of the quantum spin hall effect qsh in 1980. Jul 03, 2015 video abstract for the article quantum spin hall effect in ivvi topological crystalline insulators by s safaei, m galicka, p kacman and r buczko s safaei et al 2015 new j. Topological insulators and the quantum spin hall effect. The quantum hall effect, a quantum phenomenon that appears in macroscopic length scale, is one of the most important topics in con quantum anomalous hall effect in magnetic topological insulators ieee conference publication. We find that in inversionasymmetric systems there appears a gapless phase between the qsh and insulator phases in 3d which is in contrast with the 2d case. Prospect of quantum anomalous hall and quantum spin hall. Topological insulators topological insulator surface states experiment. When the thickness of the quantum well is varied, the electronic state changes from a normal to an inverted type at a critical. Therefore if a material is in the topological insulator state they frequently call it the quantum spin hall state. The quantum anomalous hall effect qahe is a quantized hall effect that occurs at zero magnetic field.
Quantum spin hall effect and topological phase transition in hgte quantum wells. Mele department of physics and astronomy, university of pennsylvania, philadelphia, pennsylvania 19104, usa received 22 june 2005. It has long been expected that qhe can be realized without an external magnetic field such that the effect can be applied in electric devices that consume little energy. Topological insulators tis, which exist in two and three dimensions, represent a new electronic phase stemming from the topological character of the bulk wave functions of certain materials and compounds. Topological insulators can be realised in both two dimensions 2d and in three dimensions 3d, and are nonmagnetic insulators in the bulk that. While the anomalous hall effect requires a combination of magnetic polarization and spinorbit coupling to generate a finite hall voltage even in the absence of an external magnetic field hence called anomalous, the quantum anomalous hall effect is its. Mapping the relationship between two quantum effects known. Phase transition between the quantum spin hall and insulator. Here, we predict a new largegap qsh insulator with bulk direct band gap of. Quantum spin hall effect and topological insulators. Nikolic,1 and chingray chang2, 1department of physics and astronomy, university of delaware, newark, delaware 197162570, usa. Physics the quantum hall effect gets more practical.
Quantum anomalous hall effect in 2d organic topological insulators z. When the spinorbit coupling soc is strong enough to invert the conduction and valence bands in the material,,,, it creates a new state of matter, known as the timereversalinvariant z 2 topological insulators tis. Valley polarized quantum hall effect and topological. They are also called quantum spin hall systems, because they are the gapped analogues of spin hall systems, just as the quantum hall effect is to the hall effect. 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 effect and topological phase transition. Quantum anomalous hall effect and related topological. In the quantum hall effect the longitudinal conductance vanishes while the hall conductance. Quantum spin hall effect and topological insulators request pdf. Tomonagaluttinger liquid in the edge channels of a. The intrinsic spinorbit coupling induces the quantum spin hall insulating qshi phase gapped around the fermi energy. This chapter begins with a description of quantum spin hall systems, or topological insulators, which embody a new quantum state of matter theoretically proposed in 2005 and experimentally observed later on using various methods.
Nov, 2014 whereas electrons usually have a mass, in the case of topological insulators the conducting electrons on the surface have no mass and are automatically spin polarized, leading to the unique halfinteger quantum hall effect observed and also making the material promising for various potential applications. Keywords quantum spin hall effect, spintronic devices, topological insulators. Surface quantum hall effect a perpendicular magnetic. The spin hall effect has been observed in gaas 3,4. 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. Ingap states of magnetic impurity in quantum spin hall. These include the quantum spinhall effect, nonlocal edge transport, backscattering of helical edge and surface states, weak antilocalization, unconventional triplet pwave superconductivity, topological bound states, and emergent majorana fermions in josephson junctions as well as superconducting klein tunneling. Dissipationless quantum spin current at room temperature. Further stability studies of the edge liquid through which conduction takes place in the quantum spin hall state proved. Quantum spin hall effect time reversal symmetry and edge states experiment. The quantum hall effect qhe is a quantum phenomenon that occurs on a macroscopic length scale as the result of the nontrivial topological property of a twodimensional electron system in a strong magnetic field. Quantum anomalous hall insulators goldhabergordon group. Topological insulators tis are promising for achieving dissipationless transport devices due to the robust gapless states inside the insulating bulk gap.
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. Quantum spin hall systems and topological insulators iopscience. In topological insulators, spin orbit coupling and timereversal symmetry combine to form a novel state of matter predicted to have exotic physical properties. Since 2007, the realization of quantum spin hall effect qshe in the hgtecdte 2d ti system, brought a new impetus to construct qahe. Its mechanism and properties are different from those of conventional quantum hall effects qhes induced by magnetic field. 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.
Quantum anomalous hall effect in magnetic topological. The major challenge currently is to find suitable materials for this topological state. Nov, 2014 topological insulators could bring future computing platforms based on spintronics. The hallmark of a topological insulator is the existence of metallic surface states that are higherdimensional analogues of the edge states that characterize a quantum spin hall insulator3,4,5,6. The quantum hall effect qhe is one of the most striking phenomena in the field of condensed matter physics since its discovery in the 1980s 1. The different topological sectors within a given topological insulator superconductor can be labeled by an integer winding number or a z2 quantity. The quantum spin hall effect and topological insulators xiaoliang qi and shoucheng zhang in topological insulators, spinorbit coupling and timereversal symmetry combine to form a novel state of matter predicted to have exotic physical properties. Topological insulators promising for spintronics, quantum.
Inspired by the fractional quantum hall effect, spin liquids, and fractional chern insulators, we develop a wave function approach to a new class of topological order in a twodimensional crystal. To overcome the limitations imposed by the low spinorbit. This represents the colloidal analogue of the quantum spin hall effect 21, in which electrons of opposite spins move in different directions along the same edge. The time reversal symmetry breaking on the surface can be realized by ising type magnetic moments oriented along the surface normal. Quantum spin hall effect and spin bott index in a quasicrystal lattice huaqing huang1 and feng liu1,2, 1department of materials science and engineering, university of utah, salt lake city, utah 84112, usa 2collaborative innovation center of quantum matter, beijing 84, china received 15 june 2018. Unlike the conventional qsh effect, the hqsh effect survives the breaking of. Topological phase transition and quantum spin hall edge. Quantum anomalous hall effect is the quantum version of the anomalous hall effect. 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. Whereas electrons usually have a mass, in the case of topological insulators the conducting electrons on the surface have no mass and are automatically spin polarized, leading to the unique halfinteger quantum hall effect observed and also making the material promising for various potential applications. Topological insulators and applications to quantum. Quantum spin hall effect in ivvi topological crystalline. Conventional computers use the presence and absence of electric charges to represent ones and zeroes in a.
Colloidal topological insulators communications physics. Quantum spin hall effect in iv vi topological crystalline. Request pdf quantum spin hall effect and topological insulators topological insulators tis, which exist in two and three dimensions, represent a new electronic phase stemming from the. The discovery of the quantum hall effect has proven that topology is an imperative element of the quantum description of condensed matter systems. It is distinguished from a band insulator by a z 2 topological invariant 6, analogous to the tknn invariant of the integer quantum hall effect 7. Mapping the relationship between two quantum effects known as. Given the closely related topological relation between these two quantum phenomena, it is argued that the helical edge state in the qshe regime can be viewed as two copies of the qahe channels with opposite.
Trinvariant insulators z 2 2d quantum spin hall insulator 3d topological insulators qah strategies heavyatom adlayers on magnetic substrates other ideas summary. Inverse quantum spin hall effect generated by spin pumping. Hughes,1 shoucheng zhang1 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. Controlling topological electronic structure of multifunctional mxene layer.
Topological phase transition in hgte quantum wells b. We envision that the quantum spin hall effect should be observed in 111oriented thin films of snse and snte topological crystalline insulators. Superconducting proximity effect, majorana fermions. From the quantum hall effect to topological insulators. The original motivation of great interest to topological insulators was the hope to observe the quantum spin hall effect. Qsh was the first example of a quantum state with spontaneously broken symmetry, meaning it comprises of a symmetric probability distribution where any pair of outcomes has the same probability of occurring.
In topological insulators, spinorbit coupling and timereversal symmetry combine to form a novel state of matter predicted to have exotic physical properties. Higher dimensional quantum hall effect as aclass topological. New quantum effect enables electrons to flow rapidly through. Abstract phase transitions between the quantum spin hall qsh and the insulator phases in three dimensions 3d are studied. We propose a new class of semiconductor systems based on multilayer brokengap quantum wells, in which the qshi gap reaches 60 mev and remains. Topological insulator surface states and electrical transport. Magnetic topological insulators and quantum anomalous hall effect. Topological insulators could bring future computing platforms based on spintronics. At very low temperatures and under strong magnetic fields, thin films of semiconducting materials can display a phenomenon known as the quantum hall qh effect, which can allow electrons to flow. Half quantum spin hall effect on the surface of weak. 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. A topological dirac insulator in a quantum spin hall phase. Wang, zheng liu, and feng liu department of materials science and engineering, university of utah, salt lake city, utah 84112, usa received 28 september 2012.
Unlike the conventional qsh effect, the hqsh effect survives the breaking of timereversal symmetry. After that i will describe the kane and mele model 11 for the quantum spin hall e ect in graphene and discuss its relation to a general quantum spin hall system. The quantum hall effect is an example of a phenomenon having topological features that can be observed in certain materials under harsh and stringent laboratory conditions large magnetic field, near absolute zero temperature. Exotic spintransport phenomena, such as the dissipationless quantum spin hall effect, have been speculated to originate from a topological order whose identification requires a spinsensitive. Quantum spin hall effect in 2d topological insulators. Z2 topological order and the quantum spin hall effect.
The experimental realization of the qahe effect in magnetically doped topological insulators ti thin films concludes the decade. About a decade ago, the time reversal symmetric counterpart of quantum hall effect, quantum spin hall effect, was theoretically proposed and experimentally discovered 14. Wu s, fatemi v, gibson q d, watanabe k, taniguchi t, cava r j and jarilloherrero p 2018 observation of the quantum spin hall effect up to 100 kelvin in a monolayer crystal science 359 769. Such a spin hall insulator would be of intrinsic interest, since it would allow for spin currents to be generated without dissipation. Z2 topological insulator in d 2, and its generalization in d 3. It is referred to as integer quantum hall effect as. A quantum spin hall insulator in two dimensions, also known as a topological insulator, is a topological state of matter, present in a system with spin orbit coupling, where symmetry protected dissipationless spin polarized currents counterpropagate on the sample edges, while the bulk of the sample remains insulating fig.
Quantum spin hall systems and topological insulators. Using a tightbinding approach supported by firstprinciples calculations of the band structures, we demonstrate that in these films the energy gaps in the twodimensional band spectrum depend in an oscillatory fashion on the layer. Inspired by the fractional quantum hall effect, spin liquids, and fractional chern insulators, we develop a wave function approach to a new class of topological order in. Feb, 2009 a topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetrybased classification of condensed matter. May 04, 2015 a superconducting quantum hall system is predicted to be a chiral topological superconductor, which can be used to realize topological quantum computinga quantum computing approach that is naturally robust against quantum decoherence. This pair of helical hinge modes are localized on the hinges of the top and bottom surfaces of the afm ti multilayers. Since then, topological states of matter have been vigorously investigated see refs. The discovery of the integer quantum hall effect in twodimensional electron gas opens a window to explore topological phases in quantum matter 1,2. The quantum spin hall effect and topological insulators xiaoliang qi is a research associate at the stanford institute for materials and energy science and shoucheng zhang is a professor of physics at stanford university in stanford, california. Oct 17, 2014 at very low temperatures and under strong magnetic fields, thin films of semiconducting materials can display a phenomenon known as the quantum hall qh effect, which can allow electrons to flow. The quantum spin hall qsh insulators 46 have a similar, but distinct, nontrivial topological property. Under such circumstances we consider the emergence of shibalike bound states driven by the superconducting proximity effect.
Quantum anomalous hall effect topological insulators. Researchers at princeton university have taken a step forward in the development of a new class of materials, discovering a new quantum effect that enables electrons to dash through the interior of topological dirac semimetals with very little resistance. Inverse quantum spin hall effect generated by spin pumping from precessing magnetization into a graphenebased twodimensional topological insulator sonhsien chen,1,2, branislav k. Theoretical predictions of the intrinsic spin hall effect science 2003, prl 2004. 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. To study this phenomenon, scientists apply a large magnetic field to a 2d sheet semiconductor. Edge states and integer quantum hall effect in topological. Quantum hall effect and topological magnetoelectric effect 1.
But the large field needed for the quantum hall effect would destroy most superconducting states. New family of quantum spin hall insulators in twodimensional. Observation of unconventional quantum spin textures in. 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. Topological insulators are insulating in the bulk but have gapless edgesurface states, which carry a pure spin current. In 2d topological insulators, magnetic order breaks the symmetry between the counterpropagating helical edge states, and as a result, the quantum spin hall effect can evolve into the qah effect. Video abstract for the article quantum spin hall effect in ivvi topological crystalline insulators by s safaei, m galicka, p kacman and r buczko s safaei et al 2015 new j. The half quantum hall effect is responsible for the topological magnetoelectric effect of the strong ti.
Recent theoretical and experimental studies suggest that a new class of quantum halllike topological phases can exist in spinorbit materials without external magnetic fields, with interest centering on two examples. Quantum spin hall insulator with a large bandgap, dirac. However, currently realized twodimensional 2d tis, quantum spin hall qsh insulators, suffer from ultrahigh vacuum and extremely low temperature. Quantum spin hall effect pdf the quantum hall state, a topologically nontrivial state of matter h. Apr 24, 2008 the hallmark of a topological insulator is the existence of metallic surface states that are higherdimensional analogues of the edge states that characterize a quantum spin hall insulator3,4,5,6. 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. Quantum spin hall effect and topological insulators i. Largegap quantum spin hall insulator in single layer. The deutsche physikalische gesellschaft dpg with a tradition extending back to 1845 is the largest physical society in the world with more than 61,000 members. Largegap quantum spin hall insulators in tin films yong xu,1,2 binghai yan,3 haijun zhang,1 jing wang,1 gang xu,1 peizhe tang,2 wenhui duan,2 and shoucheng zhang1,2, 1department of physics, mccullough building, stanford university, stanford, california 943054045, usa 2institute for advanced study, tsinghua university, beijing 84, peoples republic of china. Quantum spin hall effect and spin bott index in a quasicrystal lattice. In a separate paper, kane and mele introduced a topological invariant which characterizes a state as trivial or nontrivial band insulator regardless if the state exhibits or does not exhibit a quantum spin hall effect. Then i will present laughlins original model 16 for the quantum hall e ect and brie y discuss its limitations.
Quantum spin hall insulators are twodimensional materials that host conducting helical electron states strictly confined to the onedimensional boundaries. 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. On the theoretical front, it was understood that intrinsic ahe is related to berry. Yet, it has taken 25 years to be experimentally realized, which has now. The realization of qahe brings new hopes for many other novel quantum phenomena, such as topological magnetoelectric effect, image magnetic monopoles, and majorana states. Graphene, the quantum spin hall effect and topological insulators. Introduction topological classification of insulators edge states with and wo time reversal symmetry ii. The landau levels for dirac electrons are special, however, because a landau level is guaran. Quantum hall effect and topological insulators joint. Topological insulator and the quantum anomalous hall effect.
427 854 435 78 522 1395 64 1220 296 541 980 1041 426 58 451 1432 795 1222 76 111 1032 1234 1204 1059 731 450 186 148 926 979 1368 490 250 291 1131 1185 804