理学院专题学术讲座 | Wang Yang：Topological Septet Pairing in Spin-3/2 Semimetals and Chiral Majorana Modes in p±is Superconductors

Time10:30-11:30 AM, Friday, December 27, 2019

Venue: Room 311, Building 4, Yunqi Campus, Westlake University

Host: Dr. Jian Li, PI of School of Science, Westlake University

Dr. Wang Yang

University of British-Columbia

Dr. Wang Yang's research interest is in theoretical condensed matter physics. He works on strongly correlated one dimensional physics, including applications of conformal field theory and bosonization to one dimensional systems, and spin dynamics in integrable spin chains. He also works on multicomponent topological superconductivity, and chiral Majorana fermions in unconventional superconductors. Dr. Wang Yang is currently a postdoc fellow in University of British Columbia working with Prof. Ian Affleck. He obtained a Ph.D. degree from University of California San Diego in 2018 supervised by Prof. Congjun Wu, and a Bachelor of Science degree from Tsinghua University in 2012.

Multi-component electronic systems are not rare in solid state physics due to the multi-orbital band structure and spin-orbit coupling. They exhibit richer structures of topological superconductivity beyond the conventional scenarios of spin singlet and triplet pairings. We generalize the 3He-B type isotropic p-wave topological pairing to the 4-component fermion systems, which are effectively described by spin-3/2 fermions. The p-wave triplet and f-wave septet pairings are identified as topologically non-trivial characterized by large topological indices and exhibiting high order Majorana-Dirac surface spectra. Recently, there has been experimental evidence of nodal spin-3/2 superconductivity in the half-Heusler compound YPtBi semi-metal with theoretically proposed p-wave septet pairing gap function. Zero energy Majorana flat bands on the (111)-surface and their signatures in the quasi-particle interference patterns are calculated. In addition, we also discuss how to realize the chiral Majorana modes by a "kink on boundary" method starting with a degenerate Fermi surface without spin-orbit coupling. The p\pm is superconductors develop spontaneous magnetizations on the surfaces. Along the magnetic domain walls on the surface, the chiral Majorana modes propagate uni-directionally, which can be controlled by external magnetic fields.

References:

[1] Wang Yang, Yi Li, Congjun Wu, Topological septet pairing with spin-3/2 fermions -- high partial-wave channel counterpart of the He 3-B phase", Phys. Rev. Lett. 117, 075301 (2016).

[2] Wang Yang, Tao Xiang, and Congjun Wu, Majorana surface modes and nodal topological pairings in spin-3/2 semimetals", Phys. Rev. B 94, 144154 (2017).

[3] Wang Yang, Chao Xu, and Congjun Wu, Spontaneous surface magnetization and chiral Majorana modes in the p±is superconductors", arxiv:1711.05241.