Speaker: Yuan Yao (ISSP&RIKEN)

Date & Time: Dec 9, 2020, 2-3pm (JST).

Zoom link: Please register from the form below.

Title: Lieb-Schultz-Mattis ingappabilities for discrete symmetries revisited

Abstract: We will revisit quantum many-body systems with lattice translation and discrete onsite symmetries by a boundary-condition twisting approach, which is inaccessible by flux-insertion arguments. Under the twisted boundary condition, there is an exact degeneracy of ground states if the unit cell forms a projective representation of the onsite discrete symmetry. Furthermore, by a quantum-transfer-matrix formalism, we argue that such an exact degeneracy will imply ingappabilities --- a symmetric unique ground state being forbidden in the thermodynamic limit --- under conventional periodic boundary conditions. Our result produces an alternative interesting way to understand known ingappabilities. In the talk, I will also point out the missing part in the arguments, which is mathematically non-rigorous although physically reasonable. The relation of the result with the field-theory interpretations will be made clear as well.