Symmetry Protected and Topologically Protected Crossed Andreev Reflection

Abstract: Crossed Andreev reflection (CAR) is considered to probe the non-locality of the Majorana quasiparticles in topological superconductors. We propose here to study the CAR in multiband one-dimensional (1D) topological superconductors which may or may not have chiral symmetries, and show how the CAR can be applied to identify Majorana modes in such systems. In particular, for a multiband 1D topological superconductor with approximate chiral symmetry, both the multiple Majorana and low-energy Andreev bound modes can drive the nearly zero-bias CAR, which is shown to be protected by the chiral symmetry and is stable against non-magnetic disorder scatterings. The emergence of symmetry protected CAR makes it hard to identify exotic Majorana fermions out of low-energy Andreev bound states. It is interesting that the magnetic disorders, which break chiral symmetry, can fully kill the non-locality of low-energy Andreev bound states, while cannot affect the Majorana modes, leading to the topologically protected CAR which is solely contributed by the Marjorana modes. The experimentally relevant systems, including the semiconductor nanowires and the Fe chains in the top of an $s$-wave superconductor, have been considered.