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1.
Nano Lett ; 20(1): 709-714, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31838853

RESUMO

Magnetic topological insulator, a platform for realizing quantum anomalous Hall effect, axion state, and other novel quantum transport phenomena, has attracted a lot of interest. Recently, it is proposed that MnBi2Te4 is an intrinsic magnetic topological insulator, which may overcome the disadvantages in the magnetic doped topological insulator, such as disorder. Here we report on the gate-reserved anomalous Hall effect (AHE) in the MnBi2Te4 thin film. By tuning the Fermi level using the top/bottom gate, the AHE loop gradually decreases to zero and the sign is reversed. The positive AHE exhibits distinct coercive fields compared with the negative AHE. It reaches a maximum inside the gap of the Dirac cone, and its amplitude exhibits a linear scaling with the longitudinal conductance. The positive AHE is attributed to the competition of the intrinsic Berry curvature and the extrinsic skew scattering. Its gate-controlled switching contributes a scheme for the topological spin field-effect transistors.

2.
Phys Rev Lett ; 123(19): 195503, 2019 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-31765180

RESUMO

Topological insulators (TIs), featured by a symmetry-protected gapless surface Dirac cone(s) in their complete energy band gaps, have been extended from condensed-matter physics to classical bosonic systems in the last decade. However, acoustic TIs in three dimensions remain elusive because of a lack of a spin or polarization degree of freedom for longitudinal airborne sound. Here, we experimentally demonstrate a feasible way to hybridize an acoustic TI in three dimensions based on band inversion through a three-dimensional (3D) hybrid Dirac point (HDP). Such a 3D HDP, with linear dispersion in the layer plane while quadratic out of the layer, is distinct from a general point with linear dispersion in all directions. Interestingly, a single nearly gapless conical-like dispersion for acoustic surface states can be achieved at both zigzag and armchair interfaces, supporting robust sound transport. Our findings can serve as a tabletop platform for exploring unique acoustic applications based on the two-dimensional topological interfaces.

3.
Phys Rev Lett ; 122(17): 173901, 2019 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-31107095

RESUMO

Recent progress on Floquet topological phases has shed new light on time-dependant quantum systems, among which one-dimensional (1D) Floquet systems have been under extensive theoretical research. However, an unambiguous experimental observation of these 1D Floquet topological phases is still lacking. Here, by periodically bending an ultrathin metallic array of coupled corrugated waveguides, a photonic Floquet simulator was well designed and successfully fabricated to mimic the periodically driven Su-Schrieffer-Heeger model. Intriguingly, under moderate driven frequencies, we report the first observation of the anomalous Floquet topological π mode, propagating along the array's boundary. The different evolutionary behaviors between static and nonstatic topological end modes have been clearly demonstrated by the microwave near-field experiment. Furthermore, the experiment in the fast-driving regime also reveals the universal high-frequency behavior in driven systems. Our photonic simulator can serve as a versatile testing ground for various phenomena related to time-dependant 1D quantum phases, such as Thouless pumping and dynamical localization.

4.
Nat Commun ; 9(1): 4555, 2018 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-30385775

RESUMO

Topological valley states at the domain wall between two artificial crystals with opposite valley Chern numbers offer a feasible way to realize robust wave transport since only broken spatial symmetry is required. In addition to the valley, spin and crystal dimension are two other important degrees of freedom, particularly in realizing spin-related topological phenomena. Here we experimentally demonstrate that it is possible to construct two-dimensional acoustic topological pseudospin-valley coupled saddle surface states, designed from glide symmetry in a three-dimensional system. By taking advantage of such two-dimensional surface states, a full set of acoustic pseudospins can be realized, exhibiting pseudospin-valley dependent transport. Furthermore, due to the hyperbolic character of the dispersion of saddle surface states, multi-directional anisotropic controllable robust sound transport with little backscattering is observed. Our findings may open research frontiers for acoustic pseudospins and provide a satisfactory platform for exploring unique acoustic topological properties in three-dimensional structures.

5.
Nat Commun ; 9(1): 4071, 2018 10 04.
Artigo em Inglês | MEDLINE | ID: mdl-30287820

RESUMO

The two-dimensional topological insulators host a full gap in the bulk band, induced by spin-orbit coupling (SOC) effect, together with the topologically protected gapless edge states. However, it is usually challenging to suppress the bulk conductance and thus to realize the quantum spin Hall (QSH) effect. In this study, we find a mechanism to effectively suppress the bulk conductance. By using the quasiparticle interference technique with scanning tunneling spectroscopy, we demonstrate that the QSH candidate single-layer 1T'-WTe2 has a semimetal bulk band structure with no full SOC-induced gap. Surprisingly, in this two-dimensional system, we find the electron-electron interactions open a Coulomb gap which is always pinned at the Fermi energy (EF). The opening of the Coulomb gap can efficiently diminish the bulk state at the EF and supports the observation of the quantized conduction of topological edge states.

6.
ACS Nano ; 12(2): 1537-1543, 2018 02 27.
Artigo em Inglês | MEDLINE | ID: mdl-29294273

RESUMO

We report the study of a triaxial vector magnetoresistance (MR) in nonmagnetic (Bi1-xInx)2Se3 nanodevices at the composition of x = 0.08. We show a dumbbell-shaped in-plane negative MR up to room temperature as well as a large out-of-plane positive MR. MR at three directions is about in a -3%:-1%:225% ratio at 2 K. Through both the thickness and composition-dependent magnetotransport measurements, we show that the in-plane negative MR is due to the topological phase transition enhanced intersurface coupling near the topological critical point. Our devices suggest the great potential for room-temperature spintronic applications in, for example, vector magnetic sensors.

7.
J Phys Condens Matter ; 29(3): 035601, 2017 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-27845928

RESUMO

We propose using ultracold atoms trapped in a one-dimensional periodically driven optical lattice to realize the Harper-Kitaev model, where the on-site energies are periodically kicked. Such a system provides a natural platform to study both Chern insulators and Majorana fermions. Based on calculating the quasienergy spectra, we find that both Floquet Majorana modes and Hall chiral edge modes could appear at the sample boundary in the gaps between the quasienergy bands. We also study the competition of topological superconductor and Chern insulator states in the model. We calculate the [Formula: see text] index and Floquet Chern number to characterize the above two different topological states, including the topological phase transitions in the kicked Harper-Kitaev model with the increase in the strength of the kick.

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