Plasma resonance and remaining Josephson coupling in the ``decoupled vortex liquid phase'' in layered superconductors

We relate the frequency of the plasma resonance in layered superconductors with the frequency dependent superconducting response along the c-direction. We demonstrate that the sharp resonance can persist even when the global superconducting coherence in this direction is absent provided the resonance frequency is larger than the typical frequency of interlayer phase slips. In this situation the plasma frequency is determined by the average Josephson energy, which can be calculated using the high temperature expansion. We also find the temperature dependence of the average Josephson energy from the Monte Carlo simulations of the uniformly frustrated XY model and determine the applicability region of the high temperature expansion. The field and temperature scaling of the plasma frequency suggested by the high temperature expansion is consistent with experiment.Comment: slightly revised version, RevTeX, 4 pages, 2 Postscript figure

Effective dark matter fluid with higher derivative corrections

The effective field theory for hydrodynamics allows to write the action functional for fluid. In this paper, some simplest possible higher derivative terms in the fluid action and the cosmological consequences of their presence are considered. Particular attention is given to dark matter, modelled as a dust with higher derivative corrections. We study the conditions of absence of singularities in the solutions of the background and perturbed equations and investigate the evolution of perturbations in two simple models of matter dominated Universe. There is a range of parameters describing the higher derivative terms, in which the short-wavelength perturbations of dark matter are suppressed and the dark matter can be seen as fairly homogeneous on a sufficiently small scale.Comment: v3: 20 pages, 2 figures, clarified several points, in section 4 added discussion on the sensitivity of the effective dark matter fluid to various h.d. corrections, results unchange

Non-adiabatic perturbations in multi-component perfect fluids

The evolution of non-adiabatic perturbations in models with multiple coupled perfect fluids with non-adiabatic sound speed is considered. Instead of splitting the entropy perturbation into relative and intrinsic parts, we introduce a set of symmetric quantities, which also govern the non-adiabatic pressure perturbation in models with energy transfer. We write the gauge invariant equations for the variables that determine on a large scale the non-adiabatic pressure perturbation and the rate of changes of the comoving curvature perturbation. The analysis of evolution of the non-adiabatic pressure perturbation has been made for several particular models.Comment: 11 pages, v2, major revision, some clarifications added, English is improved, results unchange

Linear magnetoconductivity in multiband spin-density-wave metals with nonideal nesting

In several parent iron-pnictide compounds the resistivity has an extended range of linear magnetic field dependence. We argue that there is a simple and natural explanation of this behavior. Spin density wave transition leads to Fermi-surface reconstruction corresponding to strong modification of the electronic spectrum near the nesting points. It is difficult for quasiparticles to pass through these points during their orbital motion in magnetic field, because they must turn sharply. As the area of the Fermi surface affected by the nesting points increases proportionally to magnetic field, this mechanism leads to the linear magnetoresistance. The crossover between the quadratic and linear regimes takes place at the field scale set by the SDW gap and scattering rate.Comment: 5 pages, 2 figures, accepted to Phys. Rev. B, Rapid Communication

Role of in-plane dissipation in dynamics of Josephson lattice in high-temperature superconductors

We calculate the flux-flow resistivity of the Josephson vortex lattice in a layered superconductor taking into account both the inter-plane and in-plane dissipation channels. We consider the limiting cases of small fields (isolated vortices) and high fields (overlapping vortices). In the case of the dominating in-plane dissipation, typical for high-temperature superconductors, the field dependence of flux-flow resistivity is characterized by {\it three} distinct regions. As usual, at low fields the flux-flow resistivity grows linearly with field. When the Josephson vortices start to overlap the flux-flow resistivity crosses over to the regime of {\it quadratic} field dependence. Finally, at very high fields the flux-flow resistivity saturates at the c-axis quasiparticle resistivity. The intermediate quadratic regime indicates dominant role of the in-plane dissipation mechanism. Shape of the field dependence of the flux-flow resistivity can be used to extract both components of the quasiparticleComment: RevTeX, 3 pages, 1 PostScript figure, submitted to Phys. Rev.

To the study of non-Gaussianity in two-field slow-roll inflation

The general expression for the second order large scale curvature perturbation in the form of a functional over a background solution is derived. The explicit expressions was obtained for two special forms of the inflationary potential. In the considered cases, it is shown that a significant level of non-Gaussianity can be generated during the super-Hubble evolution only if nonadiabatic perturbations are non-negligible at the end of inflation.Comment: 15 pages,v2: more careful consideration in section 4, abstract and conclusion corrected, references adde

Phase diagram of Josephson junction between s and s+- superconductors in dirty limit

The s+- state in which order parameter has different signs in different bands is a leading candidate for the superconducting state in the iron based superconductors. We investigate a Josephson junction between s and s+- superconductors within microscopic theory. Frustration, caused by interaction of the s-wave gap parameter with the opposite-sign gaps of the s+- superconductor, leads to nontrivial phase diagram. When the partial Josephson coupling energy between the s-wave superconductor and one of the s+- bands dominates, s-wave gap parameter aligns with the order parameter in this band. In this case the partial Josephson energies have different signs corresponding to signs of the gap parameters. In the case of strong frustration, corresponding to almost complete compensation of the total Josephson energy, a nontrivial time-reversal-symmetry breaking (TRSB) state realizes. In this state all gap parameters become essentially complex. As a consequence, this state provides realization for so-called \phi-junction with finite phase difference in the ground state. The width of the TRSB state region is determined by the second harmonic in Josephson current, ~ sin(2\phi), which appears in the second order with respect to the boundary transparency. Using the microscopic theory, we establish range of parameters where different states are realized. Our analysis shows insufficiency of the simple phenomenological approach for treatment of this problem.Comment: 17 pages, 4 figures, submitted to Phys. Rev.

Crossing lattices, vortex chains, and angular dependence of melting line in layered superconductors

We investigate vortex structure and melting transition in very anisotropic layered superconductors at fields tilted with respect to the c-axis. We show that even a small in-plane field does not homogeneously tilt the vortex lattice but, instead, penetrates inside the superconductor in the form of Josephson vortices (JVs) similar to the Meissner state. At high c-axis magnetic field the phase field of the JV is built up from the phase perturbations created by displacements of pancake vortices. The crossing-lattices ground state leads to linear dependencies of the melting field and melting temperature on the in-plane field, in agreement with recent experimental observations. At small fields stacks of JVs accumulate additional pancake strings creating vortex rows with enhanced density. This mechanism explains the mixed chains-lattice state observed by Bitter decorations.Comment: 4 Pages, 2 Postscript figure

Ground states of the Josephson vortex lattice in layered superconductors

We consider the ground state configurations of the Josephson vortex lattice in layered superconductors. Due to commensurability effects with the layered structure, the lattice has multiple configurations, both aligned with layers and rotated at finite angle. At low fields the lattice switches between these configurations via first-order phase transitions. These transitions become more frequent at smaller fields. With increasing magnetic field a dilute lattice transforms first into a sheared dense lattice. With further increase of field, the shear deformation smoothly vanishes at a second-order phase transition.Comment: Proceedings of FIMS/ITS-NS/CTC/PLASMA 2004, Tsukuba, Japan, Nov. 24-28, 2004(3 pages, 2 figures

Magnetotransport of multiple-band nearly-antiferromagnetic metals due to "hot-spot" scattering

Multiple-band electronic structure and proximity to antiferromagnetic (AF) instability are the key properties of iron-based superconductors. We explore the influence of scattering by the AF spin fluctuations on transport of multiple-band metals above the magnetic transition. A salient feature of scattering on the AF fluctuations is that it is strongly enhanced at the Fermi surface locations where the nesting is perfect ("hot spots" or "hot lines"). We review derivation of the collision integral for the Boltzmann equation due to AF-fluctuations scattering. In the paramagnetic state, the enhanced scattering rate near the hot lines leads to anomalous behavior of electronic transport in magnetic field. We explore this behavior by analytically solving Boltzmann transport equation with approximate transition rates. This approach accounts for return scattering events and is more accurate than the relaxation-time approximation. The magnetic-field dependences are characterized by two very different field scales, the lower scale is set by the hot-spot width and the higher scale is set by the total scattering amplitude. A conventional magnetotransport behavior is limited to magnetic fields below the lower scale. In the wide range in between these two scales the longitudinal conductivity has linear dependence on the magnetic field and the Hall conductivity has quadratic dependence. The linear dependence of the diagonal component reflects growth of the Fermi-surface area affected by hot spots proportional to the magnetic field. We discuss applicability of this theoretical framework for describing of anomalous magnetotransport properties in different iron pnictides and selenides in the paramagnetic state.Comment: 16 pages, 7 figures, subm. Phys. Rev.