25 research outputs found

    Weak Charge Quantization on Superconducting Islands

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    We consider the Coulomb blockade on a superconductive quantum dot strongly coupled to a lead through a tunnelling barrier and/or normal diffusive metal. Andreev transport of the correlated pairs leads to quantum fluctuations of the charge on the dot. These fluctuations result in exponential renormalization of the effective charging energy. We employ two complimentary ways to approach the problem, leading to the coinciding results: the instanton and the functional RG treatment of the non-linear sigma model. We also derive the charging energy renormalization in terms of arbitrary transmission matrix of the multi-channel interface.Comment: 21 pages, 4 eps figures, RevTe

    Vortex-line liquid phases: Longitudinal superconductivity in the lattice London model

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    We study the vortex-line lattice and liquid phases of a clean type-II superconductor by means of Monte Carlo simulations of the lattice London model. Motivated by a recent controversy regarding the presence, within this model, of a vortex-liquid regime with longitudinal superconducting coherence over long length scales, we directly compare two different ways to calculate the longitudinal coherence. For an isotropic superconductor, we interpret our results in terms of a temperature regime within the liquid phase in which longitudinal superconducting coherence extends over length scales larger than the system thickness studied. We note that this regime disappears in the moderately anisotropic case due to a proliferation, close to the flux-line lattice melting temperature, of vortex loops between the layers.Comment: 8 pages, Revtex, with eps figures. To appear in Phys. Rev.

    Two-loop approximation in the Coulomb blockade problem

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    We study Coulomb blockade (CB) oscillations in the thermodynamics of a metallic grain which is connected to a lead by a tunneling contact with a large conductance g0g_0 in a wide temperature range, ECg04eg0/2<T<ECE_Cg_0^4 e^{-g_0/2}<T<E_C, where ECE_C is the charging energy. Using the instanton analysis and the renormalization group we obtain the temperature dependence of the amplitude of CB oscillations which differs from the previously obtained results. Assuming that at T<ECg04eg0/2T < E_Cg_0^4 e^{-g_0/2} the oscillation amplitude weakly depends on temperature we estimate the magnitude of CB oscillations in the ground state energy as ECg04eg0/2E_Cg_0^4 e^{-g_0/2}.Comment: 10 pages, 3 figure

    Strong 3D correlations in vortex system of Bi2212:Pb

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    The experimental study of magnetic flux penetration under crossed magnetic fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO) reveals remarkable field penetration pattern alteration (flux configuration change) and superconducting current anisotropy enhancement by the in-plane field. The anisotropy increases with the temperature rise up to Tm=54±2KT_m = 54 \pm 2 K. At T=TmT = T_m an abrupt change in the flux behavior is found; the correlation between the in-plane magnetic field and the out-of-plane magnetic flux penetration disappears. No correlation is observed for T>TmT > T_m. The transition temperature TmT_m does not depend on the magnetic field strength. The observed flux penetration anisotropy is considered as an evidence of a strong 3D - correlation between pancake vortices in different CuO planes at T<TmT < T_m. This enables understanding of a remarkable pinning observed in Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure

    Flux Creep and Flux Jumping

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    We consider the flux jump instability of the Bean's critical state arising in the flux creep regime in type-II superconductors. We find the flux jump field, BjB_j, that determines the superconducting state stability criterion. We calculate the dependence of BjB_j on the external magnetic field ramp rate, B˙e\dot B_e. We demonstrate that under the conditions typical for most of the magnetization experiments the slope of the current-voltage curve in the flux creep regime determines the stability of the Bean's critical state, {\it i.e.}, the value of BjB_j. We show that a flux jump can be preceded by the magneto-thermal oscillations and find the frequency of these oscillations as a function of B˙e\dot B_e.Comment: 7 pages, ReVTeX, 2 figures attached as postscript file

    Quantum superconductor-metal transition

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    We consider a system of superconducting grains embedded in a normal metal. At zero temperature this system exhibits a quantum superconductor-normal metal phase transition. This transition can take place at arbitrarily large conductance of the normal metal.Comment: 13 pages, 1 figure include

    Superconductor-Insulator Transition in a Capacitively Coupled Dissipative Environment

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    We present results on disordered amorphous films which are expected to undergo a field-tuned Superconductor-Insulator Transition.The addition of a parallel ground plane in proximity to the film changes the character of the transition.Although the screening effects expected from "dirty-boson" theories are not evident,there is evidence that the ground plane couples a certain type of dissipation into the system,causing a dissipation-induced phase transition.The dissipation due to the phase transition couples similarly into quantum phase transition systems such as superconductor-insulator transitions and Josephson junction arrays.Comment: 4 pages, 4 figure

    Non-linear Response of the trap model in the aging regime : Exact results in the strong disorder limit

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    We study the dynamics of the one dimensional disordered trap model presenting a broad distribution of trapping times p(τ)1/τ1+μp(\tau) \sim 1/\tau^{1+\mu}, when an external force is applied from the very beginning at t=0t=0, or only after a waiting time twt_w, in the linear as well as in the non-linear response regime. Using a real-space renormalization procedure that becomes exact in the limit of strong disorder μ0\mu \to 0, we obtain explicit results for many observables, such as the diffusion front, the mean position, the thermal width, the localization parameters and the two-particle correlation function. In particular, the scaling functions for these observables give access to the complete interpolation between the unbiased case and the directed case. Finally, we discuss in details the various regimes that exist for the averaged position in terms of the two times and the external field.Comment: 27 pages, 1 eps figur

    Anomalous diffusion, Localization, Aging and Sub-aging effects in trap models at very low temperature

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    We study in details the dynamics of the one dimensional symmetric trap model, via a real-space renormalization procedure which becomes exact in the limit of zero temperature. In this limit, the diffusion front in each sample consists in two delta peaks, which are completely out of equilibrium with each other. The statistics of the positions and weights of these delta peaks over the samples allows to obtain explicit results for all observables in the limit T0T \to 0. We first compute disorder averages of one-time observables, such as the diffusion front, the thermal width, the localization parameters, the two-particle correlation function, and the generating function of thermal cumulants of the position. We then study aging and sub-aging effects : our approach reproduces very simply the two different aging exponents and yields explicit forms for scaling functions of the various two-time correlations. We also extend the RSRG method to include systematic corrections to the previous zero temperature procedure via a series expansion in TT. We then consider the generalized trap model with parameter α[0,1]\alpha \in [0,1] and obtain that the large scale effective model at low temperature does not depend on α\alpha in any dimension, so that the only observables sensitive to α\alpha are those that measure the `local persistence', such as the probability to remain exactly in the same trap during a time interval. Finally, we extend our approach at a scaling level for the trap model in d=2d=2 and obtain the two relevant time scales for aging properties.Comment: 33 pages, 3 eps figure

    Big, Fast Vortices in the d-RVB theory of High Temperature Superconductivity

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    The effect of proximity to a Mott insulating phase on the superflow properties of a d-wave superconductor is studied using the slave boson-U(1) gauge theory model. The model has two limits corresponding to superconductivity emerging either out of a 'renormalized fermi liquid' or out of a non-fermi-liquid regime. Three crucial physical parameters are identified: the size of the vortex \textit{as determined from the supercurrent it induces;} the coupling of the superflow to the quasiparticles and the 'nondissipative time derivative' term. As the Mott phase is approached, the core size as defined from the supercurrent diverges, the coupling between superflow and quasiparticles vanishes, and the magnitude of the nondissipative time derivative dramatically increases. The dissipation due to a moving vortex is found to vary as the third power of the doping. The upper critical field and the size of the critical regime in which paraconductivity may be observed are estimated, and found to be controlled by the supercurrent length scale
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