Hirai Daigorou, Fukui Atsuhito, Sagayama Hajime, Hasegawa Takumi, Hiroi Zenji
Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan.
J Phys Condens Matter. 2022 Nov 16;51(3). doi: 10.1088/1361-648X/aca05e.
The 5pyrochlore oxide superconductor CdReO(CRO) has attracted significant interest as a spin-orbit-coupled metal (SOCM) that spontaneously undergoes a phase transition to an odd-parity multipole phase by breaking the spatial inversion symmetry due to the Fermi liquid instability caused by strong spin-orbit coupling. Despite the significance of structural information during the transition, previous experimental results regarding lattice deformation have been elusive. We have conducted ultra-high resolution synchrotron radiation x-ray diffraction experiments on a high-quality CRO single crystal. The temperature-dependent splitting of the 0 0 16 and 0 0 14 reflections, which are allowed and forbidden, respectively, in the high-temperature cubic phase I (space group-3), has been clearly observed and reveals the following significant facts: inversion symmetry breaking and tetragonal distortion occur simultaneously at= 201.5(1) K; the previously believed first-order transition between phase II (-42) and phase III (422) at∼120 K consists of two close second-order transitions at= 115.4(1) K and∼ 100 K; there is a new orthorhombic phase XI (222) in between. The order parameters (OPs) of these continuous transitions are uniquely represented by a two-dimensional irreducible representationof thepoint group, and the OPs of phase XI are a linear combination of those of phases II and III. Each phase is believed to correspond to a distinct odd-parity multipole order, and the complex successive transitions observed may be the result of an electronic phase transition that resolves the Fermi liquid instability in the SOCM.
五元烧绿石氧化物超导体CdReO（CRO）作为一种自旋轨道耦合金属（SOCM）引起了广泛关注，由于强自旋轨道耦合导致的费米液体不稳定性，它会自发地经历一个相变，转变为奇宇称多极相，打破空间反演对称性。尽管在转变过程中结构信息很重要，但先前关于晶格变形的实验结果却难以捉摸。我们对高质量的CRO单晶进行了超高分辨率同步辐射X射线衍射实验。清晰地观察到了0 0 16和0 0 14反射峰随温度的分裂，这两个反射峰在高温立方相I（空间群-3）中分别是允许和禁戒的，揭示了以下重要事实：反演对称性破缺和四方畸变在 = 201.5(1) K时同时发生；先前认为在120 K时相II（-42）和相III（422）之间的一级相变由在 = 115.4(1) K和100 K的两个紧密的二级相变组成；在它们之间存在一个新的正交相XI（222）。这些连续相变的序参量（OPs）由点群的二维不可约表示唯一表示，相XI的OPs是相II和相III的OPs的线性组合。每个相被认为对应于一个独特的奇宇称多极序，观察到的复杂连续相变可能是解决SOCM中费米液体不稳定性的电子相变的结果。
