Electronic Topological Transition in Ag2Te at High-pressure.

Yuhang Zhang,Yuwei Li,Hui Wang,Xin Wang,Yanmei Ma,Guanghui Li,Yan Li,Xuecheng Shao,Pinwen Zhu,Tian Cui

doi:10.1038/srep14681

Abstract

Recently, Ag2Te was experimentally confirmed to be a 3D topological insulator (TI) at ambient pressure. However, the high-pressure behaviors and properties of Ag2Te were rarely reported. Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa. Before ETT, the positive pressure coefficient of bulk band-gap, which is firstly found in TIs family, is found by both first-principle calculations and in situ high-pressure resistivity measurements. The electrical resistivity obtained at room temperature shows a maximum at 1.8 GPa, which is nearly 3.3 times to that at ambient pressure. This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure. Furthermore, the high-pressure structural behavior of Ag2Te has been investigated by in situ high-pressure synchrotron powder X-ray diffraction technique up to 33.0 GPa. The accurate pressure-induced phase transition sequence is firstly determined as P21/c → Cmca → Pnma. It is worth noting that the reported isostructural P21/c phase is not existed, and the reported structure of Cmca phase is corrected by CALYPSO methodology. The second high-pressure structure, a long puzzle to previous reports, is determined as Pnma phase. A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

Highlights

It is known that silver telluride crystallizes in the monoclinic system with space group P21/c (β-Ag2Te) under ambient conditions[1,2]
The second structural transition emerged at 11.3 GPa with a new peak marked at 2θ = 1 4.3°, and the characteristic peak of the second high-pressure phase become gradually stronger as the pressure increases to 19.2 GPa (see Supplementary Fig. S5(a,b))
For applying the technological devices with 3D topological insulator (TI), one of the most important goals is the control of the 2D electrical conduction in the surface of these materials[25]

Summary

Introduction

It is known that silver telluride crystallizes in the monoclinic system with space group P21/c (β-Ag2Te) under ambient conditions[1,2]. Β-Ag2Te was reported as a 3D topological insulator (TI), which acts as insulators in its bulk while has metallic Dirac fermions on its surface[6,7,8]. Pressure-induced electronic topological transition (ETT) transforms Sb2Se3, BiTeI, and As2Te3 from insulators into TIs12–16. It is interesting to further investigate the high-pressure structural behaviors for Ag2Te. Besides, in order to meet the technological application of 3D TIs, a good bulk insulating character is necessary. It is important to explore the electrical transport property of β-Ag2Te by applying pressure, in order to find a better candidate for implementing devices with 3D TIs. Here, we report an enhanced topological nature and determination of high-pressure crystal structures for Ag2Te by in-situ high-pressure resistivity measurements up to 28.4 GPa and room-temperature www.nature.com/scientificreports/. Synchrotron angle-dispersive X-ray diffraction (ADXRD) measurements up to 33.0 GPa, using a diamondanvil cell (DAC), in conjunction with first-principles calculations

Methods

Results

Conclusion