Features of the melting dynamics of a vortex lattice in a high-T c superconductor in the presence of pinning centers (original) (raw)

Theory of melting of vortex lattice in high Tc superconductors

Theory of melting of the vortex lattice in type II superconductors in the framework of Ginzburg -Landau approach is presented. The melting line location is determined and magnetization and specific heat jumps along it are calculated . The magnetization of liquid is larger than that of solid by 1.8% irrespective of the melting temperature, while the specific heat jump is about 6% and decreases slowly with temperature. The magnetization curves agrees with experimental results on Y BCO and Monte Carlo simulations.

Melting of the Vortex Lattice in Layered Superconductors

International Journal of Modern Physics B, 2009

The structure function of the vortex lattice of layered superconductor is calculated to one-loop order. Based on a phenomenological melting criterion concerning the Debye-Waller factor, we calculate the melting line of the vortex lattice, and compare our results to Monte Carlo simulation and experiment. We find that our results are quantitatively in good agreement with the Monte Carlo results. Moreover, our analytic calculation of the melting line of BSCCO fits the experiment reasonably well in a temperature range not far from Tc.

Dynamic melting and decoupling of the vortex lattice in layered superconductors

Physical Review B, 1998

The dynamic phase diagram of vortex lattices driven in disorder is calculated in two and three dimensions. A modified Lindemann criterion for the fluctuations of the distance of neighboring vortices is used, which unifies previous analytic approaches to the equilibrium and non-equilibrium phase transitions. The temperature shifts of the dynamic melting and decoupling transitions are found to scale inversely proportional to large driving currents. A comparison with two-dimensional simulations shows that this phenomenological approach can provide quantitative estimate for the location of these transitions.

Phase diagram of the vortex system in layered superconductors with strong columnar pinning

Physical Review B - PHYS REV B, 2005

We present the results of a detailed investigation of the low-temperature properties of the vortex system in strongly anisotropic layered superconductors with a random array of columnar pinning centers. Our method involves numerical minimization of a free energy functional in terms of the time-averaged local vortex density. It yields the detailed vortex density distribution for all local free-energy minima, and therefore allows the computation of any desired correlation function of the time-averaged local vortex density. Results for the phase diagram in the temperature vs pin concentration plane at constant magnetic induction are presented. We confirm that for very low pin concentrations, the low-temperature phase is a Bragg glass, which melts into an interstitial liquid phase via two first-order steps, separated by a Bose glass phase. At higher concentrations, however, the low-temperature phase is a Bose glass, and the melting transition becomes continuous. The transition is then c...

Vortex Lattice Melting in 2D Superconducting Networks and Films

We carry out an extensive Monte Carlo study of phase transitions in 2D superconducting networks, in an applied magnetic field, for square and honeycomb geometries. We consider both systems with a dilute vortex density 1/q, and dense systems near "full frustration" with vortex density 1/2 − 1/q. The dilute case gives the continuum limit as q → ∞, and serves as a model for a uniform superconducting film. For this dilute case, we find a transition temperature T c ∼ 1/q, at which the vortex lattice unpins from the network and forms a "floating solid" phase. At a higher temperature T m , this floating solid melts into a vortex liquid. We analyze the transition at T m according to the Kosterlitz-Thouless theory of dislocation mediated melting in 2D. While we find a discontinuous jump in the vortex shear modulus at T m which is consistent with this theory, we find (in opposition to this theory) that the transition is weakly first order, and we find no evidence for a hexatic liquid phase. For the case near full frustration, we find that the system can be described in terms of the density of defects in an otherwise fully frustrated vortex pattern. These dilute defects result in similar behavior as that found in the dilute vortex system, with pinned, floating, and liquid defect phases.

Freezing transition of the vortex liquid in a layered superconductor

Physica C: Superconductivity, 2001

The self-consistent theory of Singwi, Tosi, Land, and Sj olander is used to describe the liquid±solid phase in a layered superconductor in the limit of weak interplane correlation eects as would be applicable to BSCCO materials. We calculate the local-®eld corrections, static structure factor, and pair correlation function and compare our results with other methods. The Hansen±Verlet criterion is used to estimate the freezing temperature of the vortex system.

Vortex Lattice Melting in Layered Superconductors with Periodic Columnar Pins

Physical Review Letters, 2001

The melting transition of the vortex lattice in highly anisotropic, layered superconductors with commensurate, periodic columnar pins is studied in a geometry where magnetic field and columnar pins are normal to the layers. Thermodynamic properties and equilibrium density distributions are obtained from numerical minimizations of an appropriate free-energy functional. We find a line of first-order transitions that ends at a critical point as the pin concentration is increased. A simple Landau theory providing a semi-quantitative explanation of the numerical results is proposed. 74.60.Ge,74.60.Jg,85.40.Ux,74.25.Ha,74.76.Db

Phase diagram of vortex matter in layered superconductors with tilted columnar pinning centers

Physical Review B, 2009

We study the vortex matter phase diagram of a layered superconductor in the presence of columnar pinning defects, tilted with respect to the normal to the layers. We use numerical minimization of the free energy written as a functional of the time averaged vortex density of the Ramakrishnan-Yussouff form, supplemented by the appropriate pinning potential. We study the case where the pin density is smaller than the areal vortex density. At lower pin concentrations, we find, for temperatures of the order of the melting temperature of the unpinned lattice, a Bose glass type phase which at lower temperatures converts, via a first order transition, to a Bragg glass, while, at higher temperatures, it crosses over to an interstitial liquid. At somewhat higher concentrations, no transition to a Bragg glass is found even at the lowest temperatures studied. While qualitatively the behavior we find is similar to that obtained using the same procedures for columnar pins normal to the layers, there are important and observable quantitative differences, which we discuss.

The phase diagram of vortex matter in layered superconductors with tilted columnar pinning centers

2009

We study the vortex matter phase diagram of a layered superconductor in the presence of columnar pinning defects, tilted with respect to the normal to the layers. We use numerical minimization of the free energy written as a functional of the time averaged vortex density of the Ramakrishnan-Yussouff form, supplemented by the appropriate pinning potential. We study the case where the pin density is smaller than the areal vortex density. At lower pin concentrations, we find, for temperatures of the order of the melting temperature of the unpinned lattice, a Bose glass type phase which at lower temperatures converts, via a first order transition, to a Bragg glass, while, at higher temperatures, it crosses over to an interstitial liquid. At somewhat higher concentrations, no transition to a Bragg glass is found even at the lowest temperatures studied. While qualitatively the behavior we find is similar to that obtained using the same procedures for columnar pins normal to the layers, th...

Continuous Two-Dimensional Melting of Vortex-Solid in High Temperature Superconductors

MRS Proceedings, 1989

A model of continuous two-dimensional melting in the mixed state of high temperature superconductors is proposed. Two-dimensional melting sets in at a cross-over temperature Tx(H) below the three-dimensinal phase transition Tx(H) due to finite size effects, and Tx(H) is a function of the sample thickness (lc), applied magnetic field (H), and k(= λ/ξ) For a given zero-field transition temperature Tc0 and material properties, (such as defect density), the onset temperature of 2D-melting (Tx(H)) decreases with decreasing sample thickness and increasing magnetic field. In transport studies, thermally induced melting is further complicated by the depinning effect of high current densities.