Special Condensed Matter Seminar, Chaoxing Liu, Penn State, “Possible realization of bosonic symmetry protected topological phases in bilayer graphe

Tue, Mar 8, 2016, 1:30 pm to 2:30 pm
PCTS Seminar Room
Ever since the discovery of time reversal invariant topological insulators, intensive research interests are focused on how to identify new topological phases that are protected by symmetry (known as symmetry protected topological states) and how to search for new topological materials to realize these topological phases. A large variety of topological materials have been theoretically proposed for topological states in free fermion systems and many of them have been confirmed experimentally. In contrast, few topological materials have been for bosonic symmetry protected topological (BSPT) states, which normally require strong interactions, in two or higher dimensions. In this talk, I would like to propose the possible realization of BSPT phases in two existing topological material systems. One is to consider the zero Landau levels of bilayer graphene under a strong magnetic field and the other is the thin film of topological mirror Kondo insulators, such as SmB6. Our strategy is to first construct two copies of helical edge modes, which are protected by either spin Chern number or mirror Chern number, at the boundary of these two systems at the free fermion level. Then, by introducing strong interactions into this system, we find that the interaction can gap out all the local fermion degrees of freedom and the remaining degrees of freedom are of bosonic type, consistent with BSPT phases. This strategy allows us to conclude that BSPT phases are highly likely to be realized in these two topological material systems. I will also briefly discuss possible experimental signatures and the difference between these two topological material systems. Reference: [1] Bilayer Graphene as a platform for Bosonic Symmetry Protected Topological States, Zhen Bi, Ruixing Zhang, Yi-Zhuang You, Andrea Young, Leon Balents, Chao-Xing Liu, Cenke Xu, arXiv:1602.03190v1