Abstract

In this talk we will discuss a new type of topolgoical defects — momentum vortices — in spiral spin liquids and recent experimental identification of them. Spiral spin liquids are a class of spin liquids that feature a ring degeneracy of its ground states in momentum space. Over the years, a concrete physical picture of its spin liquid nature has not been established, considering that its zero-temperature ground states do not admit any local degeneracy. We illustrate the low-energy structure of 2D spiral spin liquids, and reveal its connection to fracton and smectic physics. We find that the local momentum vector can form new types of momentum vortices in the system, which have very different properties from the commonly known spin vortices [1]. Their proliferation leads the system into the spin liquid phase at low temperature. Furthermore, the effective theory shows that these objects are equivalent to quadrupoles of fractons in rank-2 U(1) gauge theory and also topological defects in smectic matter. I will also discuss related materials [2] and recent experimental identification of the momentum vortices [3].

[1] H. Yan and J. Reuther, Low energy structure of spiral spin liquids, Phys. Rev. Research 4, 023175 (2022) R. Pohle, H. Yan and N. Shannon, Phys. Rev. B 104 , 024426 M. Gonzalez et al., arXiv: 2404.00100 [2] S. Gao et al., Spiral spin-liquid on a honeycomb lattice, Phys. Rev. Lett. 128, 227201 C. Balz et al., Nat. Phys. 12, 942–949 (2016). [3] Spiral Spin Liquid Noise, arXiv:2405.02075