Time: 10:30 am (UTC/GMT+08:00, Beijing/Shanghai), Sep. 16 (Wed.), 2020
Online Meeting Room (zoom.com): Click here to join the meeting
Meeting ID: 927 2754 4138
Speaker: Fan ZHANG (UT Dallas)
Abstract:
Recently, a novel class of topological insulators/superconductors (TI/TS) coined "higher-order (HO) TI/TS” has become a major topic at the forefront of condensed matter physics. A HO TI/ TS hosts protected gapless states on boundaries of more than one dimensions lower, and in this talk we will tour three prototypes proposed in 2012, 2018, and 2020, respectively. Special emphases will be their original motivations and experimental impacts. By introducing a domain wall method that is commonly used nowadays, the 2012 theory based on Bi2Se3 features an extrinsic chiral hinge mode [PRL 110, 046404 (2013)]. The 2018 platform exploits Fe-based superconductors and stabilizes intrinsic Majorana (true) corner modes [PRL 121, 186801 (2018)], highlighting the general criteria for realizing Majorana Kramers pairs. The 2020 study identifies two rare pristine materials with global bulk/surface band gaps and natural helical hinge modes, i.e., Bi4I4 as an extrinsic HOTI and Bi4Br4 as an intrinsic HOTI, by revealing an overlooked role of inversion center and unifying all TI with helical edge/surface/ hinge modes [arXiv:2005.14710]. All the three models can still be valid even if all spatial symmetries were broken. (FZ acknowledges the work by all his collaborators and the support from the ARO, NSF, DOE, and DARPA in US.)
