Condensed Matter Seminars

A grand challenge in the field of topological physics is to understand the role of interaction and to realize interacting topological phases in realistic materials. In this talk, we will discuss the possible realization of interacting topological states in bilayer graphene under a strong magnetic field. We start from a fermonic two-channel quantum spin Hall state with two copies of helical edge states, which have been demonstrated experimentally in bilayer graphene. By introducing interaction into two channel helical liquids, we demonstrate that all the fermion degrees are gapped out and only one bosonic mode remains, thus yielding a bosonic version of topological insulator, dubbed “bosonic symmetry protected topological state”. Physically, the two dual boson fields of this bosonic mode carry charge-2e and spin-1, respectively, due to the helical nature. Thus, we dubbed them “bosonic helical liquids”. We further study the transport of a quantum point contact for bosonic helical liquids and compare them to fermonic two-channel helical liquids. A novel charge insulator/spin conductor phase is identified in the weak repulsive interaction regime for bosonic helical liquids while charge insulator/spin insulator or charge conductor/spin conductor phase is present for fermonic two-channel helical liquids. Thus, a quantum point contact experiment will allow us to identify the bosonic symmetry protected topological states unambiguously. Similar physics can also emerge in topological mirror Kondo insulators, such as SmB6.

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, 2016

[2] Interacting topological phases in thin films of topological mirror Kondo insulators, Rui-Xing Zhang, Cenke Xu, Chao-Xing Liu, arXiv: 1607.06073, 2016

[3] Fingerprints of bosonic symmetry protected topological state in a quantum point contact, Rui-xing Zhang, Chao-xing Liu, arxiv: 1610.01236, 2016