报告人：刘尚 博士 Physics Department of Harvard University

时  间：2018年12月21日(周五)上午10:00

摘要：We study a two-dimensional tight-binding model of a topological crystalline insulator protected by rotation symmetry. The model is built by stacking two Chern insulators with opposite Chern numbers which transform under conjugate representations of the rotation group, e.g. p+/p- orbitals. Despite its apparent similarity to the Kane-Mele model, it does not host stable gapless surface states. Nevertheless, the model exhibits topological responses including the appearance of quantized fractional charge bound to rotational defects (disclinations) and the pumping of angular momentum in response to threading an elementary magnetic flux, which are described by a mutual Chern-Simons coupling between the electromagnetic field and an effective probe field corresponding to the rotation symmetry. We show that although the filled bands of the model do not admit a symmetric Wannier representation, this obstruction is removed on addition of appropriate atomic orbitals, which implies fragile topology. As a result, the responses of the model can be derived by representing it as a superposition of atomic orbitals with positive and negative integer coefficients.

Reference: Shang Liu, Ashvin Vishwanath, Eslam Khalaf, arXiv: 1809.01636.

简历：Shang Liu is currently a PhD student at the Physics Department of Harvard University. Under the advising of Prof. Ashvin Vishwanath, his research focuses on the theory of topological phase of matter

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