p-wave Superfluidity by Spin-Nematic Fermi Surface Deformation

TL;DR

This paper investigates how spin-dependent anisotropy in a square lattice causes Fermi surface mismatch, suppressing conventional s-wave pairing and leading to the emergence of unconventional p-wave superfluidity and incommensurate density waves.

Contribution

It uncovers a rich phase diagram showing p-wave superfluidity and density waves, using Diagrammatic Monte Carlo to explore intermediate coupling regimes with strong anisotropy.

Findings

Suppression of s-wave BCS instability due to Fermi surface mismatch.

Emergence of incommensurate density wave at strong anisotropy.

Identification of two distinct p-wave superfluid states at intermediate anisotropy.

Abstract

We study attractively interacting fermions on a square lattice with dispersion relations exhibiting strong spin-dependent anisotropy. The resulting Fermi surface mismatch suppresses the s-wave BCS-type instability, clearing the way for unconventional types of order. Unbiased sampling of the Feynman diagrammatic series using Diagrammatic Monte Carlo methods reveals a rich phase diagram in the regime of intermediate coupling strength. Instead of a proposed Cooper-pair Bose metal phase [A. E. Feiguin and M. P. A. Fisher, Phys. Rev. Lett. 103, 025303 (2009)] we find an incommensurate density wave at strong anisotropy and two different p-wave superfluid states with unconventional symmetry at intermediate anisotropy.