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Register a new userProperties of the Bose glass phase in irradiated superconductors near the matching field
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Carsten Wengel
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Structural and transport properties of interacting localized flux lines in the Bose glass phase of irradiated superconductors are studied by means of Monte Carlo simulations near the matching field B_Phi, where the densities of vortices and columnar defects are equal. For a completely random columnar pin distribution in the xy-plane transverse to the magnetic field, our results show that the repulsive vortex interactions destroy the Mott insulator phase which was predicted to occur at B = B_Phi. On the other hand, for ratios of the penetration depth to average defect distance lambda/d <= 1, characteristic remnants of the Mott insulator singularities remain visible in experimentally accessible quantities as the magnetization, the bulk modulus, and the magnetization relaxation, when B is varied near B_Phi. For spatially more regular disorder, e.g., a nearly triangular defect distribution, we find that the Mott insulator phase can survive up to considerably large interaction range lambda/d, and may thus be observable in experiments.
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Magneto-optical imaging in YBa2Cu3O7-d with tilted columnar defects (CDs) shows an asymmetric critical-state field profile. The observed hysteretic shift of the profile ridge (trough) from the center of the sample is explained by in-plane magnetization originated from vortex alignment along CDs. The extracted ratio of the in-plane to out-of-plane magnetization component has a maximum at 1/5 of matching field ($B_Phi$) and disappears above $B_Phi/3$, suggesting a reduction of interlayer coherence well bellow $B_Phi$ in the Bose glass phase. Implications are discussed in comparison with the vortex liquid recoupling observed in irradiated Bi2Sr2CaCu2O8+y.
Using an extensive scaling analysis of the transport properties in twinned YBaCuO(123) crystals we have experimentally found the predicted change in the universality class of the Bose-glass to liquid transition when the magnetic field is applied at small angles away from the direction of the correlated defects. The new dynamical critical exponent is s=1.1 +/-0.2.
The structural correlation functions of a weakly disordered Abrikosov lattice are calculated in a functional RG-expansion in $d=4-epsilon$ dimensions. It is shown, that in the asymptotic limit the Abrikosov lattice exhibits still quasi-long-range translational order described by a {it nonuniversal} exponent $eta_{bf G}$ which depends on the ratio of the renormalized elastic constants $kappa ={c}_{66}/ {c}_{11}$ of the flux line (FL) lattice. Our calculations clearly demonstrate three distinct scaling regimes corresponding to the Larkin, the random manifold and the asymptotic Bragg-glass regime. On a wide range of {it intermediate} length scales the FL displacement correlation function increases as a power law with twice the manifold roughness exponent $zeta_{rm RM}(kappa) $, which is also {it nonuniversal}. Correlation functions in the asymptotic regime are calculated in their full anisotropic dependencies and various order parameters are examined. Our results, in particular the $kappa$-dependency of the exponents, are in variance with those of the variational treatment with replica symmetry breaking which allows in principle an experimental discrimination between the two approaches.
Dynamics of vortices in strongly type-II superconductors with strong disorder is investigated within the frustrated three-dimensional XY model. For two typical models in [Phys. Rev. Lett. {bf 91}, 077002 (2003)] and [Phys. Rev. B {bf 68}, 220502(R) (2003)], a strong evidence for the finite temperature vortex glass transition in the unscreened limit is provided by performing large-scale dynamical simulations. The obtained correlation length exponents and the dynamic exponents in both models are different from each other and from those in the three-dimensional gauge glass model. In addition, a genuine continuous depinning transition is observed at zero temperature for both models. A scaling analysis for the thermal rounding of the depinning transition shows a non-Arrhenius type creep motion in the vortex glass phase, contrarily to the recent studies..
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