Zhang Mengxiang, Yuan Xinxing, Li Yue, Luo Xi-Wang, Liu Chang, Zhu Mingdong, Qin Xi, Zhang Chuanwei, Lin Yiheng, Du Jiangfeng
CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China.
CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China.
Phys Rev Lett. 2022 Dec 16;129(25):250501. doi: 10.1103/PhysRevLett.129.250501.
Triply degenerate points (TDPs), which correspond to new types of topological semimetals, can support novel quasiparticles possessing effective integer spins while preserving Fermi statistics. Here by mapping the momentum space to the parameter space of a three-level system in a trapped ion, we experimentally explore the transitions between different types of TDPs driven by spin-tensor-momentum couplings. We observe the phase transitions between TDPs with different topological charges by measuring the Berry flux on a loop surrounding the gap-closing lines, and the jump of the Berry flux gives the jump of the topological charge (up to a 2π factor) across the transitions. For the Berry flux measurement, we employ a new method by examining the geometric rotations of both spin vectors and tensors, which lead to a generalized solid angle equal to the Berry flux. The controllability of a multilevel ion offers a versatile platform to study high-spin physics, and our Letter paves the way to explore novel topological phenomena therein.
三重简并点（TDPs）对应于新型拓扑半金属，在保持费米统计的同时，能够支持具有有效整数自旋的新型准粒子。在此，通过将动量空间映射到捕获离子中三能级系统的参数空间，我们通过实验探索了由自旋张量动量耦合驱动的不同类型TDPs之间的转变。我们通过测量围绕能隙关闭线的回路中的贝里通量，观察到具有不同拓扑电荷的TDPs之间的相变，并且贝里通量的跃变给出了跨转变的拓扑电荷的跃变（相差2π因子）。对于贝里通量测量，我们采用了一种新方法，通过检查自旋矢量和张量的几何旋转，这导致一个等于贝里通量的广义立体角。多能级离子的可控性为研究高自旋物理提供了一个通用平台，我们的这篇论文为探索其中的新型拓扑现象铺平了道路。
