Experimental evidences of topological surface states of β-Ag2Te

Azat Sulaev,Qing Hua Lin,Peng Ren,Ting Yu,Caiyu Qiu,Yuan Ping Feng,Shuang-Yuan Zhang,Qingyu Wu,Shun-Qing Shen,Zhi Peng Li,Ming-Yong Han,Lan Wang,Wei Guang Zhu,Bin Xia,Lei Shen

doi:10.1063/1.4795735

Abstract

We present evidence of topological surface states in β-Ag2Te through first-principles calculations, periodic quantum interference effect and ambipolar electric field effect in single crystalline nanoribbon. Our first-principles calculations show that β-Ag2Te is a topological insulator with a gapless Dirac cone with strong anisotropy. To experimentally probe the topological surface state, we synthesized high quality β-Ag2Te nanoribbons and performed electron transport measurements. The coexistence of pronounced Aharonov-Bohm oscillations and weak Altshuler-Aronov-Spivak oscillations clearly demonstrates coherent electron transport around the perimeter of β-Ag2Te nanoribbon and therefore the existence of topological surface states, which is further supported by the ambipolar electric field effect for devices fabricated by β-Ag2Te nanoribbons. The experimental evidences of topological surface states and the theoretically predicted anisotropic Dirac cone of β-Ag2Te suggest that the material may be a promising candidate of topological insulator for fundamental study and future spintronic devices.

Highlights

Topological insulator is a state of quantum matter characterized by Z2 invariance
The existence of the A-B effect at low temperature is a fingerprint of topological surface states with weak disorder, which is related to the Dirac type Hamiltonian of the helical surface state
As aforementioned, when the electron transport evolves gradually from ballistic to diffusive with increasing disorder or scattering, the quantum oscillation in topological insulator will show a gradual transition from h/e period to h/2e period simultaneously

Summary

INTRODUCTION

Topological insulator is a state of quantum matter characterized by Z2 invariance. It is composed of a fully filled insulating bulk state and an odd number of massless spin-helical Dirac cones of twodimensional surface states.[1,2,3] Due to the fascinating new physics and great potential application in spintronics and quantum computation, topological insulator quickly becomes a trend research field in condensed matter physics. Our calculations confirmed the anisotropic topological surface state, the shape of the surface state of our calculations is different from that in the literature.[26] The existence of the surface states in Ag2Te is confirmed experimentally, based on the Aharonov-Bohm interference pattern obtained in the magnetotransport measurements at low temperatures.

BAND STRUCTURE CALCULATION

EXPERIMENT

RESULTS AND DISCUSSION

Ambipolar electric gate effect

CONCLUSION