Knowledge Bank

A system with unequal populations of up and down fermions may exhibit a Larkin-Ovchinnikov (LO) phase consisting of a periodic arrangement of domain walls where the order parameter changes sign and the excess polarization is localized. We find that the LO phase has a much larger range of stability in a lattice compared to the continuum; in a harmonic trap, the LO phase may involve 80% of the atoms in the trap, and can exist up to an entropy s ∼ 0.5kB per fermion. We discuss detection of the LO phase (i) in real space by phase-contrast imaging of the periodic excess polarization; (ii) in k space by time-of-flight imaging of the single-particle and pair-momentum distributions; (iii) in energy space from the excess density of states within the gap arising from Andreev bound states in the domain walls.