arXiv subjects

B. K. Chakraverty

Publications and source records attributed to B. K. Chakraverty.

3 recordsLinked to original sources

arXiv2002

Andreev reflection off a fluctuating superconductor in the absence of equilibrium

Andreev reflection between a normal metal and a superconductor whose order parameter exhibits quantum phase fluctuations is examined. The approach chosen is non perturbative in the tunneling Hamiltonian and enables to probe the whole range of voltage biases up to the gap amplitude. Results are illustrated using the one-dimensional Josephson- Junction Array model previously introduced in the linear response regime. Phase fluctuations are shown to affect the differential conductance and are compared to the result of Blonder, Tinkham and Klapwijk for a rigid BCS superconductor. The noise spectrum of the Andreev current is also obtained and its second derivative with respect to frequency is proposed as a direct tool to analyze the phase fluctuations.

cond-mat.supr-con↗

arXiv1999

Quantum Phase Fluctuations in High Tc Superconductors

If phase coherence determines the superconducting transition temperature Tc in the cuprate oxides, it is of great interest to understand the role that dynamics of the phase fluctuation plays in bringing about depletion of the superconducting condensate. We will show that a phase correlation function can be calculated that allows us to describe depletion of superconducting condensate as a result of the quantum fluctuation. In two dimension, dynamic phase fluctuation or pair fluctuation gives rise to a condensate depletion linear with temperature as T$\to O$ in superconductors with nodes at the fermi surface.

cond-mat.supr-con↗

arXiv1999

Effective action for Superconductors and BCS-Bose crossover

A standard perturbative expansion around the mean-field solution is used to derive the low-energy effective action for superconductors at T=0. Taking into account the density fluctuations at the outset we get the effective action where the density $ρ$ is the conjugated momentum to the phase $θ$ of the order parameter. In the hydrodynamic regime, the dynamics of the superconductor is described by a time dependent non-linear Schrödinger equation (TDNLS) for the field $Ψ(x)=\sqrt{ρ/2} e^{iθ}$. The evolution of the density fluctuations in the crossover from weak-coupling (BCS) to strong-coupling (Bose condensation of localized pairs) superconductivity is discussed for the attractive Hubbard model. In the bosonic limit, the TDNLS equation reduces to the the Gross-Pitaevskii equation for the order parameter, as in the standard description of superfluidity. The conditions under which a phase-only action can be derived in the presence of a long-range interaction to describe the physics of the superconductivity of ``bad metals'' are discussed.

cond-mat.supr-con↗