Vortex Lattice Structure of Fulde-Ferrell-Larkin-Ovchinnikov Superconductors

In superconductors with singlet pairing, the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is expected to be stabilized by a large Zeeman splitting. We develop an efficient method to evaluate the Landau-Ginzburg free energies of FFLO-state vortex lattices and use it to simplify the considerations that determine the optimal vortex configuration at different points in the phasediagram. We demonstrate that the order parameter spatial profile is completely determined, up to a uniform translation, by its Landau level index n and the vortex Lattice structure and derive an explicit expression for the order parameter spatial profile that can be used to determine n from experimental data.Comment: 6 pages with one embedded color figure. Minor changes. Final version as publishe

Fluctuation-Driven First-Order Transition in Pauli-limited d-wave Superconductors

We study the phase transition between the normal and non-uniform (Fulde-Ferrell-Larkin-Ovchinnikov) superconducting state in quasi two-dimensional d-wave superconductors at finite temperature. We obtain an appropriate Ginzburg-Landau theory for this transition, in which the fluctuation spectrum of the order parameter has a set of minima at non-zero momenta. The momentum shell renormalization group procedure combined with dimensional expansion is then applied to analyze the phase structure of the theory. We find that all fixed points have more than one relevant directions, indicating the transition is of the fluctuation-driven first order type for this universality class.Comment: 5 page

Josephson Effect in Fulde-Ferrell-Larkin-Ovchinnikov Superconductors

Due to the difference in the momenta of the superconducting order parameters, the Josephson current in a Josephson junction between a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor and a conventional BCS superconductor is suppressed. We show that the Josephson current may be recovered by applying a magnetic field in the junction. The field strength and direction at which the supercurrent recovery occurs depend upon the momentum and structure of the order parameter in the FFLO state. Thus the Josephson effect provides an unambiguous way to detect the existence of an FFLO state, and to measure the momentum of the order parameter.Comment: 4 pages with one embedded eps figur