arXiv subjects

Carsten Wengel

Publications and source records attributed to Carsten Wengel.

4 recordsLinked to original sources

arXiv1998

Properties of the Bose glass phase in irradiated superconductors near the matching field

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 λ/d, and may thus be observable in experiments.

cond-mat.supr-con↗

arXiv1997

Dynamical universality classes of the superconducting phase transition

We present a finite temperature Monte Carlo study of the XY-model in the vortex representation, and study its dynamical critical behavior in two limits. The first neglects magnetic field fluctuations, corresponding to the absence of screening, which should be a good approximation in high $T_c$ superconductors ($κ\to \infty$) except extremely close to the critical point. Here, from finite size scaling of the linear resistivity we find the dynamical critical exponent of the vortex motion to be $z\approx 1.5$. The second limit includes magnetic field fluctuations in the strong screening limit ($κ\to 0$) corresponding to the true asymptotic inverted XY critical regime, where we find the unexpectedly large value $z\approx 2.7$. We compare these results, obtained from dissipative dynamics in the vortex representation, with the universality class of the corresponding model in the phase representation with propagating (spin wave) modes. We also discuss the effect of disorder and the relevance of our results for experiments.

cond-mat.supr-con↗

arXiv1997

A common Universality class for the three-dimensional Vortex Glass and Chiral Glass?

We present a Monte Carlo study of the d=3 gauge glass and the XY--spin glass models in the vortex representation. We investigate the critical behavior of these models by a scaling analysis of the linear resistivity and current-- voltage characteristics, both in the limits of zero and strong screening of the vortex-interactions. Without screening, both models show a glass transition at a finite temperature and, within the numerical accuracy, exhibit the same critical exponents: z approx 3.1 and nu=1.3 +- 0.3. With strong screening, the finite temperature glass transition is destroyed in both cases and the same exponent nu=1.05 +- 0.1 is found at the resulting zero temperature transition.

cond-mat.supr-con↗

arXiv1996

Weakly Pinned Bose Glass vs. Mott Insulator Phase in Superconductors

We study the properties of the Bose glass phase of localized flux lines in irradiated superconductors near the matching field $B_Φ$. Repulsive vortex interactions destroy the Mott insulator phase predicted to occur at $B=B_Φ$. For ratios of the penetration depth to average defect distance $λ/ d \leq 1$ remnants of the Mott insulator singularities remain visible in the magnetization, the bulk modulus, and the magnetization relaxation, as B is varied near $B_Φ$. For $λ\geq d$, the ensuing weakly pinned Bose glass is characterized by a soft Coulomb gap in the distribution of pinning energies.

cond-mat.supr-con↗