Zhang Yuhang, Li Yan, Ma Yanmei, Li Yuwei, Li Guanghui, Shao Xuecheng, Wang Hui, Cui Tian, Wang Xin, Zhu Pinwen
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.
Sci Rep. 2015 Sep 30;5:14681. doi: 10.1038/srep14681.
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.
最近，实验证实Ag2Te在常压下是一种三维拓扑绝缘体（TI）。然而，Ag2Te的高压行为和性质鲜有报道。在此，首次在Ag2Te中于1.8 GPa处发现了压力诱导的电子拓扑转变（ETT）。在ETT之前，通过第一性原理计算和原位高压电阻率测量，在TI家族中首次发现了体带隙的正压力系数。室温下获得的电阻率在1.8 GPa处出现最大值，几乎是常压下的3.3倍。这一结果表明，在此压力下可获得Ag2Te最佳的体绝缘特性和拓扑性质。此外，利用原位高压同步辐射粉末X射线衍射技术研究了Ag2Te高达33.0 GPa的高压结构行为。首次准确确定了压力诱导的相变序列为P21/c→Cmca→Pnma。值得注意的是，报道的同构P21/c相并不存在，且利用CALYPSO方法对报道的Cmca相结构进行了修正。第二个高压结构，此前报道中一直存在疑问，确定为Pnma相。变温电阻率测量结果证实了Ag2Te中存在压力诱导的金属化现象。
