报告题目：Atomic line defects and topological superconductivity in unconventional superconductors
报告摘要：Topological superconductors (TSCs) are correlated quantum states with simultaneous off-diagonal long-range order and nontrivial topological invariants. They produce gapless or zero energy boundary excitations, including Majorana zero modes and chiral Majorana edge states with topologically protected phase coherence essential for fault-tolerant quantum computing. Candidate TSCs are very rare in nature. Here, we propose a novel route toward emergent quasi-one-dimensional (1D) TSCs in naturally embedded quantum structures such as atomic line defects in unconventional spin-singlet s-wave and d-wave superconductors. We show that inversion symmetry breaking and charge transfer due to the missing atoms lead to the occupation of incipient impurity bands and mixed parity spin singlet and triplet Cooper pairing of neighboring electrons traversing the line defect. Nontrivial topological invariants arise and occupy a large part of the parameter space, including the time reversal symmetry breaking Zeeman coupling due to applied magnetic field or defect-induced magnetism, creating TSCs in different topological classes with robust Majorana zero modes at both ends of the line defect. Beyond providing a novel mechanism for the recent discovery of zero-energy bound states at both ends of an atomic line defect in monolayer Fe(Te,Se) superconductors, the findings pave the way for new material realizations of the simplest and most robust 1D TSCs using embedded quantum structures in unconventional superconductors with large pairing energy gaps and high transition temperatures.
报告人简介：Yi Zhang got his Bachelor degree in physics at University of Science and Technology of China (USTC) in 2008. Then he went to Boston College for his Ph.D study under the supervision of Prof. Kevin Bedell, where his research mainly focuses on the studying of the collective modes of the magnetically ordered system using the Landau Fermi liquid theory. After he got his Ph.D in 2014, he moved to Louisiana State University to work with Prof. Mark Jarrell as a postdoctor, where mainly study the Anderson localization in disordered systems such as doped Si and diluted magnetic semiconductors. Last year in 2019, he joined KITS as a postdoctor to work with Prof. Fuchun Zhang, where my research interests shift to the study of the twisted bilayer graphene (TBG) as well as the search for the Majorana zero modes in the unconventional superconductors such as Fe-based pnictides.