Speaker: Shunsuke Furuya (Ibaraki U)

Date & Time: Jan. 20, 2021, 2-3pm (JST).

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Title: Symmetry-protected critical phases and anomaly of Wess-Zumino-Witten theories

Abstract:

The last decade has witnessed the bloom of topological classification of gapped quantum phases. The idea of protecting gapped phases by symmetries has allowed us to understand gapped quantum phases better. With an open boundary condition, the symmetry-protected topological phase is accompanied by a gapless edge mode, where symmetries guarantee the absence of the excitation gap at the edge. The symmetry protection of gapless edge modes motivates us to question if there is a symmetry-protection mechanism of the universality class of bulk gapless phases. In this talk, we will discuss our paper [1] that pointed out that there is indeed symmetry protection of bulk gapless phases in quantum spin chains. Our argument is based on spin chains' effective field theory, the SU(2) Wess-Zumino-Witten theory. We will discuss how its 't Hooft anomaly, an impediment in gauging a Z2 symmetry, classifies bulk gapless quantum phases of spin chains.

[1] SCF and M. Oshikawa, Phys. Rev. Lett. 118, 021601 (2017)