Andreev bound states at boundaries of polarized 2D Fermi superfluids with s-wave pairing and spin-orbit coupling

Two-dimensional (2D) Fermi gases subject to s-wave pairing, spin-orbit coupling and large-enough Zeeman spin splitting are expected to form a topological superfluid. While the general argument of bulk-boundary correspondence assures the existence of topologically protected zero-energy quasiparticle excitation at such a system's boundaries, it does not fully determine the physical properties of the low-energy edge states. Here we develop a versatile theoretical method for elucidating microscopic characteristics of interface-localized subgap excitations within the spin-resolved Bogoliubov-deGennes formalism. Our analytical results extend current knowledge about edge excitations existing at the boundary between vacuum and a 2D superfluid that is in its topological or nontopological regime. We also consider the Andreev bound states that emerge at an interface between coexisting time-reversal-symmetry-breaking topological and nontopological superfluids and juxtapose their unusual features with those of vacuum-boundary-induced edge excitations. Our theory provides a more complete understanding of how the spin-orbit-coupled polarized 2D Fermi gas can be tailored as a platform for realizing unconventional Majorana excitations.Comment: 37 pages, 5 figures. Submission to SciPos