Ground-state angular momentum, spectral asymmetry, and topology in chiral superfluids and superconductors

Abstract

Recently, it was discovered that the ground-state orbital angular momentum in two-dimensional chiral superfluids with pairing symmetry (px+ipy)ν depends on the winding number ν in a striking manner. The ground-state value for the ν=1 case is Lz=ℏN/2 as expected by counting the Cooper pairs, while a dramatic cancellation takes place for ν>1. The origin of the cancellation is associated with the topological edge states that appear in a finite geometry and give rise to a spectral asymmetry. Here, we study the reduction of orbital angular momentum for different potential profiles and pairing strengths, showing that the result Lz=ℏN/2 is robust for ν=1 under all studied circumstances. We study how angular momentum depends on the gap size Δ/EF and obtain the result Lz=ℏν2N(1−μEF) for ν=2,3. Thus, the gap dependence of Lz for ν<4 enters at most through the chemical potential while ν≥4 is qualitatively different. In addition, we generalize the spectral asymmetry arguments to total angular momentum in the ground state of triplet superfluids where due to a spin-orbit coupling Lz is not a good quantum number. We find that the ground-state total angular momentum also behaves very differently depending on total angular momentum of the Cooper pairs.

Source-reported materials — not catalogue approval

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