Surface Andreev bound states are found to be very common in unconventional superconductors. In the first part of my talk, I will present our studies of surface Andreev bound states in Weyl semimetal superconductors. It has been noted that certain surfaces of Weyl semimetals have bound states forming open Fermi arcs, which are never seen in typical metallic states. Our works show that the Fermi arcs enable Weyl semimetals to support exotic surface states with crossed flat bands in the superconducting state. We clarify the topological origin of the crossed flat bands and the relevant symmetry that stabilizes the cross point. We also discuss their possible experimental verification by tunneling spectroscopy. Second, I will discuss about the importance of self-consistent calculation of surface Andreev bound states. We study the influence of nonmagnetic impurity scatterings on the tunneling conductance of a junction consisting of a normal metal and a disordered unconventional superconductor. By solving the quasiclassical Eilenberger equation self-consistently, we find that the impurity scatterings in both the Born and the unitary limits affect the formation of the Andreev bound states and modify strongly the tunneling spectra around zero bias. Our results are interpreted well by the appearance of odd-frequency Cooper pairs near the interface and by the divergent behavior of the impurity self-energy. The present paper provides a useful tool to identify the pairing symmetry of unconventional superconductors in experiments.

Bo Lü was born in 1984 in Shenyang, China. He obtained his PhD in 2013 from Peking University. After finishing his postdoctoral fellowship at Nagoya University and University of Manchester, he joined Tianjin University as Special Researcher in 2018. His research focuses on Andreev reflection, Josephson effect and spintronics.