State Of Layered Superconductors Research Articles

Resonance in-plane magnetic field effect as a means to reveal the Fulde-Ferrell-Larkin-Ovchinnikov state in layered superconductors

The vector potential of a parallel magnetic field produces a modulation of the interlayer coupling between adjacent superconducting layers. In some cases the period of this modulation can coincide with the period of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulation of the superconducting order parameter. Such a resonance condition results in cusps on the temperature and in-plane angular dependencies of the upper critical field Hc2. This effect can open up a possibility to unambiguously evidence a spatially modulated superconducting phase in layered conductors. Remarkably, the proposed signature of the FFLO state is directly based on the main feature of the FFLO state, the spatial modulations of the order parameter.

A hydrodynamic approach to description of Josephson vortex dynamics in layered superconductors

A general phenomenological theory describing dynamics of Josephson vortices interacting with a variety of linear waves in layered high-Tc superconductors is developed. The theory is based on hydrodynamic long wave approximation and describes the interaction of vortices with electromagnetic, electronic and phonon degrees of freedom on an equal footing. In the limiting cases it can be reduced to simple models considered elsewhere. The proposed model is used for numerical simulation of the resistive state in layered superconductors placed in an external magnetic field. We demonstrate the excitation of electromagnetic modes in layered superconductors by a moving Josephson vortex lattice and the structural phase transitions in the vortex lattice, caused by these modes. We also show that a moving Josephson vortex lattice excites the phonon and mixed modes in layered superconductors and that its dynamics is noticeably complicated by the nonzero charge coupling.

Intrinsic pinning of vortices as a direct probe of the nonuniform Larkin-Ovchinnikov-Fulde-Ferrell state in layered superconductors.

Previously the search for the modulated superconducting Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state was performed by means of measurements which do not give direct information on spatial modulation of the superconducting state. We propose to measure interlayer conductivity in Josephson-coupled layered superconductors as a function of the strength and the orientation of the parallel magnetic field. We show that interlayer critical current and the conductivity have peaks when the magnetic field is perpendicular to the in-plane wave vector of the LOFF state and when the period of the Josephson vortex lattice induced by the magnetic field is commensurate with the LOFF period.

COLLECTIVE MODE IN JOSEPHSON-COUPLED LAYERED SUPERCONDUCTORS IN WEAK PARALLEL MAGNETIC FIELDS

We propose a theoretical model to account for the increase in the effect of both magnetic induction and presence of a nonequilibrium state in layered superconductors which behave as intrinsic Josephson junctions. Using this model, we investigate the phase dynamics with a magnetic field applied parallel to the superconducting layers and show that the increase in the coupling between the superconducting layers due to the increase in the effect of magnetic induction and the departure from equilibrium significantly modifies the dispersion of the Josephson plasma mode in intrinsic Josephson junctions from that in conventional stacks of Josephson junctions.

Superconducting State of Layered Superconductor κ-(ET)4Hg2.89Br8 Under Magnetic Field Parallel to the Conducting Plane

The upper critical field of κ-(ET)4Hg2.89Br8 was measured under a parallel magnetic field up to 24 T in the temperature region down to 0.5 K. The data obtained at 0.5 K indicate that the upper critical field tends to saturate toward 0 K but exceeds the Pauli limit by more than two times. The anisotropy of the upper critical field within the superconducting plane was not observed. The implication of the high upper critical field is discussed.

Mixed state in layered superconductors

Using a generalized Lawrence-Doniach model we develop a theory describing electromagnetic properties of layered superconductors with inequivalent layers. Our theory includes a solution for the state that the Abrikosov vortices perpendicular to the layers coexist with the Josephson vortices parallel to the layers. The magnetization process exhibits remarkable difference from those of conventional type II superconductors in the direction parallel to the layers. The first order transition at H c1 is predicted in some parameter region.

First-order phase transition to the vortex state in layered superconductors

Layered superconductors with a second order phase transition in a magnetic field parallel to the layers and a first order phase transition in a transverse field are considered. In inclined field the first order phase transition to the vortex state is predicted. A new type of intermediate state with the coexistence of normal and vortex regions is shown to exist.

On the possibility of a first-order phase transition to the vortex state in layered superconductors

Layered superconductors with a second-order phase transition in a magnetic field parallel to the layers and a first-order phase transition in a perpendicular field are considered. In the case of an inclined field a first-order phase transition to the vortex state is predicted. A new type of intermediate state with the coexistence of normal and vortex regions is shown to exist.

Effects of impurities on the nonuniform state in layered superconductors

The possibility of the existence of a nonuniform state is investigated, and the nature of the phase transition is determined in layered superconductors with Josephson-like interlayer coupling as a function of sample purity and temperature for a field parallel to the layers. The dependence of the upper critical field HK2(‖) on temperature and electron mean free path within the layers is obtained. At temperatures T < 0.55 Tc, it is shown that depending on the purity of the superconductor and the temperature, either a second-order phase transition into a nonuniform superconducting state or a first-order transition into a uniform superconducting state is observed in layered superconductors with Josephson interlayer coupling for a field parallel to the layers.