Emergent symmetry in lithium molybdate (LMO)

Upon cooling, condensed matter systems typically transition into states of lower symmetry. While the converse, i.e. the emergence of higher symmetry at lower temperatures, has been hypothesized, it is extremely rare. Here, we show how an unusually isotropic 25 magnetoresistance in the highly anisotropic, one-dimensional conductor Li0.9Mo6O17 (LMO), and its temperature dependence, can be interpreted as a renormalization group (RG) flow towards a so-called separatrix. This approach is equivalent to an emergent symmetry in the system. The existence of two distinct ground states – Mott insulator and superconductor – can then be traced back to two opposing RG trajectories. By establishing a direct link between quantum field theory 30 and an experimentally measurable quantity, we uncover a path through which emergent symmetry might be identified in other candidate materials.

凝聚态系统在降温过程中通常会转变为低对称性物态。反之，尽管已有假说提出低温下会涌现高对称性，但此类情况极为罕见。本文阐明：在高度各向异性的一维导体Li₀.₉Mo₆O₁₇（LMO）中，异常各向同性的磁阻（对应原文第25行标注）及其温度依赖性，可被诠释为朝向所谓重整化群（Renormalization Group，RG）流分界线的流动。该诠释图景等价于该系统中的涌现对称性。两种截然不同的基态——莫特绝缘体（Mott insulator）与超导体——的存在，可追溯至两条截然相反的重整化群轨迹。通过在量子场论（Quantum Field Theory，对应原文第30行标注）与可实验测量的物理量之间建立直接关联，我们揭示了一条可在其他候选材料中识别涌现对称性的可行路径。