اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNonuniversal Correlations and Crossover Effects in the Bragg-Glass Phase of Impure Superconductors
118
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
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.
قيم البحث
اقرأ أيضاً
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..
Monte Carlo simulations of layered BSCCO samples are used to investigate the behavior of vortex matter at low fields, particularly in connection with the possible occurrence of a Bragg glass (BrG) phase at low density of columnar defects, a phenomeno
n characterized by the prevalence of short-range over long-range order. In this dislocation-free topological phase the translational order correlation function displays a power law decay. For magnetic induction $B=0.1$ kG the analysis of the data for the first Bragg peak of the planar structure factor, the hexatic order parameter, and the Delaunay triangulation shows that, as the density of columnar defects is lowered, a textit{crossover} (or transition) from Bose glass to BrG phase takes place in this textit{highly anisotropic} high-T${}_c$ superconductor. Most importantly, an analysis of the {low-temperature} 3D vortex-vortex correlation function in terms of the structure factor, calculated via a saddle point approach and the use of the numerical data as input, provides clear-cut evidence of {the} power law decay of the {divergent} Bragg peaks in the BrG phase, a fundamental feature that was inequivocally verified only in isotropic compounds.
Via molecular dynamics simulations of a generic glass former in the supercooled and normal liquid states, it is shown that spatial correlations of strain fluctuations exhibit a crossover from the well-established power-law $sim 1/r^3$-decay at long w
avelengths to an exponential behavior, $sim exp(-r/l_{text {c}})$ at intermediate distances. The characteristic length of the exponential decay grows both with temperature and time via, $l_{text {c}}^2 propto D(T), t$, with $D(T)$ being the temperature-dependent diffusion coefficient. This suggests that the crossover between the power-law and exponential decays is governed by a diffusion process.
Using large scale Monte Carlo simulations on a uniformly frustrated 3DXY model, we report a first order vortex lattice melting transition in clean, isotropic extreme type-II $kappa to infty$ superconductors. This work clarifies an important issue: th
e unpinned vortex liquid is always incoherent with no phase coherence in any directions for all anisotropies. Previous claims of a disentangled vortex liquid for isotropic superconductors based on simulations, are due to finite size effects. We explicitly show that the effective vortex-line tension vanishes precisely at the superconducting phase transition in zero magnetic field. This loss of line tension is accompanied by an abrupt change in the connectivity of the vortex tangle across the superconductor. We also obtain results indicating that the connectivity of the vortex tangle changes in a similar way even in finite magnetic field, and suggest that this could also be associated with a genuine phase-transition.
Large-scale simulations have been performed on the current-driven two-dimensional XY gauge glass model with resistively-shunted-junction dynamics. It is observed that the linear resistivity at low temperatures tends to zero, providing strong evidence
of glass transition at finite temperature. Dynamic scaling analysis demonstrates that perfect collapses of current-voltage data can be achieved with the glass transition temperature $T_{g}=0.22$, the correlation length critical exponent $ u =1.8$, and the dynamic critical exponent $ z=2.0$. A genuine continuous depinning transition is found at zero temperature. For creeping at low temperatures, critical exponents are evaluated and a non-Arrhenius creep motion is observed in the glass phase.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
