Mesoscopic phase separation in anisotropic superconductors

Abstract

General properties of anisotropic superconductors with mesoscopic phase separation are analysed. The main conclusions are as follows: Mesoscopic phase separation can be thermodynamically stable only in the presence of repulsive Coulomb interactions. Phase separation enables the appearance of superconductivity in a heterophase sample even if it were impossible in pure-phase matter. Phase separation is crucial for the occurrence of superconductivity in bad conductors. Critical temperature for a mixture of pairing symmetries is higher than the critical temperature related to any pure gap-wave symmetry of this mixture. In bad conductors, the critical temperature as a function of the superconductivity fraction has a bell shape. Phase separation makes the single-particle energy dispersion softer. For planar structures phase separation suppresses d-wave superconductivity and enhances s-wave superconductivity. These features are in agreement with experiments for cuprates.

Optimum inhomogeneity of local lattice distortions in La 2 CuO 4+ y

“…Our quantitative results should be tested against theories of composite, granular superconductors proposed for cuprates (10,14,15,25,(30)(31)(32)(55)(56)(57)(58)(59)(60)(61)(62). The X-ray data indicate that these theories must take into account not only the usual superconducting proximity effects, but also the effects of the strains the two components exert on each other.…”

Non-conventional superconducting fluctuations in Ba(Fe1−xRhx)2As2 iron-based superconductors

“…[1][2][3][4][5][6] Among all the experimental tools, the measure of the magnetization 7-10 is the most straightforward, as it gives a clear diamagnetic response M f l , as soon as the Cooper pairs are formed, provided to subtract possible paramagnetic contributions, occurring at a temperature above the onset of the fluctuations. In this regard, the Ginzburg-Landau (GL) theory predicts, for evanescent fields H, a diamagnetic magnetization linear in H for T ≫ T c , and accordingly a susceptibility χ dia ∝ −ǫ D/2−2 , where ǫ = (T − T c )/T c is the reduced temperature and D is the system dimensionality.…”

Normal state resistivity and excess of conductivity around the optimal doping of Bi-2212 thin films

“…This behavior may be related with the change in the carrier-carrier correlation effect by decreasing doping, in theories which have predicted that hole carriers may segregate into hole-rich and hole-poor islands [28,29]. By decreasing doping at around p = 0.1, an independent magnetic order or crossover due to the magnetic correlations in hole-poor islands may be responsible for the change of critical exponent from −1/2 to −1/3.…”