Fragility of surface states in topological superfluid 3He

Superfluid He-3, with unconventional spin-triplet p-wave pairing, provides a model system for topological superconductors, which have attracted significant interest through potential applications in topologically protected quantum computing. In topological insulators and quantum Hall systems, the surface/edge states, arising from bulk-surface correspondence and the momentum space topology of the band structure, are robust. Here we demonstrate that in topological superfluids and superconductors the surface Andreev bound states, which depend on the momentum space topology of the emergent order parameter, are fragile with respect to the details of surface scattering. We confine superfluid He-3 within a cavity of height D comparable to the Cooper pair diameter xi(0). We precisely determine the superfluid transition temperature T-c and the suppression of the superfluid energy gap, for different scattering conditions tuned in situ, and compare to the predictions of quasiclassical theory. We discover that surface magnetic scattering leads to unexpectedly large suppression of T-c, corresponding to an increased density of low energy bound states.

Automated summary

The research on surface Andreev bound states in superfluid He-3 demonstrates that they are fragile with respect to the details of surface scattering, unlike the robust surface/edge states in topological insulators and quantum Hall systems. The unexpectedly large suppression of T-c due to surface magnetic scattering leads to an increased density of low energy bound states.