We report the pressure (p_max = 1.5 GPa) evolution of the crystal structure of the Weyl semimetal T_d-MoTe_2 by means of neutron diffraction experiments. We find that the fundamental non-centrosymmetric structure T_d is fully suppressed and transforms into a centrosymmertic 1T' structure at a critical pressure of p_cr = 1.2 GPa. This is strong evidence for a pressure induced quantum phase transition (QPT) between topological to a trivial electronic state. Although the topological QPT has strong effect on magnetoresistance, it is interesting that the superconducting critical temperature T_c, the superfluid density, and the SC gap all change smoothly and continuously across p_cr and no sudden effects are seen concomitantly with the suppression of the T_d structure. This implies that the T_c, and thus the SC pairing strength, is unaffected by the topological QPT. However, the QPT requires the change in the SC gap symmetry from non-trivial s+- to a trivial s++ state, which we discuss in this work. Our systematic characterizations of the structure and superconducting properties associated with the topological QPT provide deep insight into the pressure induced phase diagram in this topological quantum material.

中文翻译：

---

外尔半金属 Td-MoTe2 中的压力诱导拓扑量子相变

我们通过中子衍射实验报告了外尔半金属 T_d-MoTe_2 晶体结构的压力 (p_max = 1.5 GPa) 演变。我们发现基本的非中心对称结构 T_d 被完全抑制，并在 p_cr = 1.2 GPa 的临界压力下转变为中心对称的 1T' 结构。这是拓扑到微电子态之间压力诱导量子相变 (QPT) 的有力证据。尽管拓扑 QPT 对磁阻有很强的影响，但有趣的是超导临界温度 T_c、超流体密度和 SC 间隙都在 p_cr 上平滑连续地变化，并且没有伴随着 T_d 结构的抑制而出现突然的影响。这意味着 T_c 以及 SC 配对强度，不受拓扑 QPT 的影响。然而，QPT 需要将 SC 间隙对称性从非平凡的 s+- 更改为平凡的 s++ 状态，我们在这项工作中对此进行了讨论。我们对与拓扑 QPT 相关的结构和超导特性的系统表征提供了对这种拓扑量子材料中压力诱导相图的深入了解。