Quantum Effects in Resistance-Shunted Josephson Junctions

TL;DR

This paper theoretically investigates the thermodynamics and transport properties of resistance-shunted Josephson junctions in the tight-binding limit, revealing a novel low-energy crossover and strongly-correlated phenomena beyond the Kondo framework.

Contribution

It introduces a phenomenological harmonic-oscillator model to analyze weak coupling regimes and uncovers a new low-energy crossover affecting various physical responses.

Findings

Identification of a new low-energy crossover in the density of states.

Discovery of strongly-correlated phenomena beyond the Kondo problem.

Analytical results on linear, optical, and nonlinear responses.

Abstract

Thermodynamics and transport properties of resistance-shunted Josephson junctions are studied theoretically in the tight-binding limit E_C/E_J<<1, where E_C and E_J are a charging energy and a Josephson coupling energy respectively. Based on a phenomenological harmonic-oscillator model, weak coupling region K=R_Q/R<<1 is analytically studied, where R and R_Q=h/(2e)^2 are a shunted resistance and the quantum resistance. In addition to the effective bandwidth, we find that this multi-level system genuinely has a novel crossover at lower energy below which the density of states becomes strongly degenerate. These two energy scales control the linear DC responses, optical responses, and nonlinear I-V characteristics. The lower energy crossover indicates the existence of a new class of strongly-correlated phenomena beyond the framework of the Kondo problem.