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Some clues in the investigation of the FFLO phase in superconductors

The Fulde–Ferrell–Larkin–Ovichinnikov (FFLO) phase is investigated in a two-dimensional superconductor described by a negative- U Hubbard model in the presence of a magnetic field. The parameter space defined by interparticle attraction and band filling is investigated and a search is performed for the FFLO phase therein, so as to provide clues to experiments designed to confirm the existence of a nonuniform spatial nature of the superconducting state. Our results convincingly demonstrate periodic modulation of the local pairing gap in real space. Heavy fermions, considered as a probable candidate that hosts the FFLO phase, are found in a metallurgically clean state and shows extreme type-II behaviour. In our calculations both these conditions are satisfied for a certain magnetic field range and the range expands for large interacting strengths and particle densities. The cleanliness condition is met as the coherence length becomes very small (compared to the mean free path) and the extreme type-II behaviour shows up via a large Ginzburg–Landau parameter.