题 目：Quantum Anomalous Semimetals
报告人：付博 博士 香港大学
时 间：2022年4月01日（星期五) 14：30
地 点：腾讯会议 ID 785-675-471
报告摘要：The topological states of matter and topological materials have been attracting extensive interests as one of the frontier topics in condensed matter physics and materials science since the discovery of quantum Hall effect in 1980s. So far all the topological phases such as quantum Hall effect, quantum spin Hall effect and topological insulators and superconductors are characterized by a nonzero integer or Z and Z2 topological invariant. Here we propose a novel type of semimetals which hosts a single cone of Wilson fermions instead of Dirac fermions. The Wilson fermions possess linear dispersion near the energy crossing point, but breaks the chiral or parity symmetry such that an unpaired Dirac cone can be realized on a lattice. They are not prohibited by the Nielsen-Ninomiya theorem and avoid the fermion doubling problem. We find that the system can be classified by the relative homotopy group, and the topological invariant is a half-integer. We term the unexpected and nontrivial quantum phase as “quantum anomalous semimetal”. The half-integer topological invariant leads to a fractional electric and electromagnetic polarization in one and three dimensions, and half-quantized Hall conductance in two and four dimensions with no well-defined boundary states, forming a novel type of the bulk-boundary correspondence in the topological phase. The topological phase is a synergy of topology of band structure in solid and quantum anomaly in quantum field theory. The work opens the door towards exploring novel states of matter with fractional topological charge.
References：
1. Bo Fu, Jin-Yu Zou, Zi-Ang Hu, Huan-Wen Wang, Shun-Qing Shen, arXiv:2203.00933.
2. Jin-Yu Zou, Bo Fu, Huan-Wen Wang, Zi-Ang Hu, Shun-Qing Shen,, arXiv:2202.08493.
3. H.-W. Wang, B. Fu, J.-Y. Zou, Z. A. Hu, S.-Q. Shen, arXiv:2202.01957.
报告人介绍：Dr. Bo Fu received his Ph.D. in condensed matter physics in 2017 under the supervision of Prof. Qunxiang Li and Prof. Qinwei Shi at the University of Science and Technology of China. Currently, he worked in Prof. Shunqing Shen’ group at the University of Hong Kong as a postdoctoral fellow. His research mainly focuses on magneto-transport theory in Dirac materials and intriguing phenomena in higher order topological insulators and superconductors.
