Spin-Charge Groups for Fermions in Fluids and Crystals

by Prof. ZhengXin Liu (刘正鑫) (Renmin University of China)

Monday 13 Apr 2026, 14:00 → 15:00 Asia/Shanghai

Tsung-Dao Lee Institute/N6F-N600 - Lecture Room (Tsung-Dao Lee Institute)

Host: Prof. Xin Liu  

Venue: TDLI Meeting Room N600

Tencent Meeting link: https://meeting.tencent.com/dm/jhlv9TmUFK6j

Meeting ID: 649105098, no password

 

Abstract:

Known symmetry groups are not sufficient to handle various couplings between spin, charge and spatial degrees of freedom for fermions. In this talk, we introduce the spin-charge groups (SCG) to describe the most general symmetries of fermionic systems. These groups are composed of the spin and charge operations as the `internal' symmetries, the spatial and temporal operations as `external' symmetries, couplings between them, and projective twists. After providing the general group structures of SCG, we study their potential applications in concrete physical systems, including $^3$He superfluids, charge-4e superconductors, collinear magnets with spin-fluxes, and superconductors with coexisting magnetic orders. We show that SCSG can give rise to extra band degeneracies, Chern numbers and cross spin-charge responses.

 

Biography:

Zheng-Xin Liu obtained his Ph.D in the Hong Kong University of Science and Technology in 2010. Then he worked in IAS of Tsinghua University for five years and joined Renmin University of China in 2015. Dr. Liu's research interest includes topological phases of matter, quantum magnetism, superconductivity, and many-body quantum computation. With collaborators, he worked out the classification of bosonic SPT phases, proposed multi-node quantum spin liquids in Kitaev systems, and classified the general symmetry groups for magnetic crystals and fermionic systems.