Electrical and Structural Behaviors of Topological Insulator

Electrical and Structural Behaviors of Topological Insulator
Ag2Te under High-pressure
Yuhang Zhang Yan Li, Yanmei Ma, Hui Wang, Tian Cui, Xin Wang, and Pinwen Zhu
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
The mineral hessite and empressite are the stable forms of silver tellurides exist naturally under
ambient conditions.1 Recently, the monoclinic Ag2Te was reported as a 3D topological insulator
whose bulk is insulating, while its surface supports metallic Dirac fermions.2 Topological insulators
may bring out exotic quantum phenomena such as Majorana fermions, magnetoelectric effect, and
quantum anomalous Hall effect.3 Pressure has been reported as a significant tool to turn the
topological insulator into a superconductor.4 Therefore, it is necessary to have a good understanding
of the effects of pressure on Ag2Te.
In this work, In situ high-pressure synchrotron powder X-ray diffraction technique has been
performed on Ag2Te, which was synthesized under high pressure and high temperature conditions,
up to 33.0 GPa. It is observed that Ag2Te exhibits a phase transition from the ambient monoclinic
structure (space group P21/c) to an orthorhombic structure (space group Cmca) at 2.2 GPa, and
starts the second transition at 11.3 GPa. The Rietveld refinement results of Ag2Te have verified that
the patterns measured at 2.2 and 2.6 GPa represented mixed phases instead of an isostructural
monoclinic phase indexed by previous report. The pressure dependence of the unit-cell volume
results revealed an increase in compressibility and the mechanism of the bulk modulus reduction
has been further discussed. Under compression, the electrical resistivity presented an intense
fluctuation in the monoclinic phase. The calculation results showed that the evolution in electrical
resistivity was related to an unconventional fluctuation in band-gap of the monoclinic Ag2Te that is
semiconductor-metal phase transition was experimentally confirmed by the temperature-dependent
resistivity results.
Keywords: DAC, ADXRD, Resistivity Measurement, First-Principles Calculations.
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