Tuning a Josephson junction through a quantum critical point

We tune the barrier of a Josephson junction through a zero-temperature metal-insulator transition and study the thermodynamic behavior of the junction in the proximity of the quantum-critical point. We examine a short-coherence-length superconductor and a barrier (that is described by a Falicov-Kimball model) using the local approximation and dynamical mean-field theory. The inhomogeneous system is self-consistently solved by performing a Fourier transformation in the planar momentum and exactly inverting the remaining one-dimensional matrix with the renormalized perturbation expansion. Our results show a delicate interplay between oscillations on the scale of the Fermi wavelength and pair-field correlations on the scale of the coherence length, variations in the current-phase relationship, and dramatic changes in the characteristic voltage as a function of the barrier thickness or correlation strength (which can lead to an ``intrinsic'' pinhole effect).

J.K. Freericks, B.K. Nikolic, P. Miller · 2001