Characteristics of First-Order Vortex Lattice Melting: Jumps in Entropy and Magnetization

We derive expressions for the jumps in entropy and magnetization characterizing the first-order melting transition of a flux line lattice. In our analysis we account for the temperature dependence of the Landau parameters and make use of the proper shape of the melting line as determined by the relative importance of electromagnetic and Josephson interactions. The results agree well with experiments on anisotropic Y$_1$Ba$_2$Cu$_3$O$_{7-\delta}$ and layered Bi$_2$Sr$_2$Ca$_1$Cu$_2$O$_8$ materials and reaffirm the validity of the London model.Comment: 4 pages. We have restructured the paper to emphasize that in the London scaling regime (appropriate for YBCO) our results are essentially exact. We have also emphasized that a major controversy over the relevance of the London model to describe VL melting has been settled by this wor

Low-Field Phase Diagram of Layered Superconductors: The Role of Electromagnetic Coupling

We determine the position and shape of the melting line in a layered superconductor taking the electromagnetic coupling between layers into account. In the limit of vanishing Josephson coupling we obtain a new generic reentrant low-field melting line. Finite Josephson coupling pushes the melting line to higher temperatures and fields and a new line shape $B_{{\rm m}} \propto (1-T/T_c)^{3/2}$ is found. We construct the low-field phase diagram including melting and decoupling lines and discuss various experiments in the light of our new results.Comment: 12 pages, 1 figure attached as compressed and uuencoded postscrip

Vortices and 2D bosons: A Path-Integral Monte Carlo Study

The vortex system in a high-T_c superconductor has been studied numerically using the mapping to 2D bosons and the path-integral Monte Carlo method. We find a single first-order transition from an Abrikosov lattice to an entangled vortex liquid. The transition is characterized by an entropy jump dS = 0.4 k_B per vortex and layer (parameters for YBCO) and a Lindemann number c_L = 0.25. The increase in density at melting is given by d\rho = 6.0*10^{-4} / \lambda(T)^2. The vortex liquid corresponds to a bosonic superfluid, with \rho_s = \rho even in the limit \lambda -> \infty.Comment: 9 pages, RevTeX, 4 PostScript figures. The entropy jump at the transition has been recomputed and is now in agreement with experiments on YBCO. Some minor modifications were made in the tex

Vortices and 2D Bosons: A Path-Integral Monte Carlo Study

The vortex system in a high-T c superconductor has been studied numerically using the mapping to 2D bosons and the Path Integral Monte Carlo method. We find a single first-order transition from an Abrikosov lattice to an entangled vortex liquid. The transition is characterized by an entropy jump of #S # 0.27k B per degree of freedom and a Lindemann number c L # 0.29. At low fields, # # a 0 , the density is reduced by ##/# # 0.0003 upon melting. The vortex liquid corresponds to a bosonic superfluid, with # s = # even in the limit # ##. PACS numbers: 74.20.De, 74.60.Ec, 05.30.Jp Typeset using REVT E X Our understanding of the phase diagram of type II superconductors has improved significantly since the mixed state was introduced by Abrikosov in 1957 [1]. The vortex state is of particular interest for the high-T c superconductors, where strong thermal fluctuations lead to melting of the vortex lattice and the appearance of a vortex liquid phase. Experimental evidence for a first order ..

Ultra-thin and lightweight photovoltaic/thermal collections for building integration

Unglazed PVT collector concepts to cover electricity and heat demands of LowEx Buildings have been experimentally and numerically evaluated. Critical aspects affecting electrical and thermal efficiency are identified. A promising solution was found in the direct lamination of thin-film solar cells onto a channel-plate thermal collector resulting in a highly efficient, super-light (<4kg/m2) and ultra-thin (<4mm) PVT collector. The lightweight design simplifies building integration and reduces the amount of materials and associated costs as well as environmental impacts.ISSN:1876-610