Exotic paired phases in ladders with spin-dependent hopping

Understand

Fermions in two-dimensions (2D) when subject to anisotropic spin-dependent hopping can potentially give rise to unusual paired states in {\it unpolarized} mixtures that can behave as non-Fermi liquids.

• One possibility is a fully paired state with a gap for fermion excitations in which the Cooper pairs remain uncondensed.
• Such a "Cooper-pair Bose-metal" phase would be expected to have a singular Bose-surface in momentum space.
• As demonstrated in the context of 2D bosons hopping with a frustrating ring-exchange interaction, an analogous Bose-metal phase has a set of quasi-1D descendent states when put on a ladder geometry.