The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase is an unconventional superconducting state found under the influence of a strong Zeeman field. This phase is identified by finite center-of-mass momenta in the Cooper pairs, causing the pairing amplitude to oscillate in real space. Repulsive correlations, on the other hand, smear out spatial inhomogeneities in
d-wave superconductors. We investigate the FFLO state in a strongly correlated
d-wave superconductor within a consolidated framework of Hartree-Fock-Bogoliubov theory and the Gutzwiller approximation. We find that the crucial effects of strong correlations lie in shifting the BCS-FFLO phase boundary towards a lower Zeeman field and thereby enlarging the window of the FFLO phase. In the FFLO state, our calculation features a sharp midgap peak in the density of states, indicating the formation of strongly localized Andreev bound states. We also find that the signatures of the FFLO phase survive even in the presence of an additional translational-symmetry-breaking competing order in the ground state. This is demonstrated by considering a broken-symmetry ground state with a simultaneous presence of the
d-wave superconducting order and a spin-density wave order, often found in unconventional superconductors.
The previously studied Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is stabilized by a magnetic field via the Zeeman coupling in spin-singlet superconductors. Here we suggest a novel route to achieve nonzero center-of-mass momentum pairing states in superconductors with Fermi surface nesting. We investigate two-dimensional superconductors under a uniform external current, proportional to a finite pair momentum of q(e). We find that an FFLO state with a spontaneous pair momentum of q(s) is stabilized above a certain critical current that depends on the direction of the external current. A finite q(s) arises in order to make the total pair-momentum of q(t)(=q(s) + q(e)) perpendicular to the nesting vector, which is independent of spin states of Cooper pairs. We also discuss experimental signatures of the FFLO state.
The Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state in asymmetric D-wave fermion superfluids is investigated generally. The angle dependence of the pairing gap (angle-dependent gap) for D-wave is also considered. Except the two special orientations of the Cooper pair momentum which are parallel/orthogonal to the symmetry-axis of ADG (called as FFLO-ADG-O and FFLO-ADG-P states), new orientations of the Cooper pair momentum between the two special ones are also found. These new orientations of the Cooper pair momentum correspond to new possible locally stable state (defined as FFLO-ADG-B state). Furthermore, the FFLO-ADG-O state is favored for small asymmetry and the FFLO-ADG-P state is located at large asymmetry, whereas the FFLO-ADG-B state is stable for moderate asymmetry. Moreover, the range of the asymmetry where the superfluids exists is enhanced strongly by taking the ADG to the FFLO state.