Universal R-C crossover in current-voltage characteristics for unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions

TL;DR

This paper investigates a universal crossover in the current-voltage characteristics of unshunted overdamped Nb-AlO_x-Nb Josephson junction arrays, revealing a temperature-independent transition between resistance-dominated and capacitance-dominated regimes.

Contribution

It demonstrates a universal, temperature-independent crossover in the CVC of Josephson junction arrays, explained by a single-plaquette RSJ model with finite capacitance.

Findings

Identification of a temperature-independent crossover current I_{cr}

Observation of resistance and capacitance dominated regimes in CVC

Theoretical explanation using single-plaquette RSJ model

Abstract

We report on some unusual behavior of the measured current-voltage characteristics (CVC) in artificially prepared two-dimensional unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions. The obtained nonlinear CVC are found to exhibit a pronounced (and practically temperature independent) crossover at some current I_{cr}=\left(\frac{1}{2\beta_C}-1\right)I_C from a resistance R dominated state with V_R=R\sqrt{I^2-I_C^2} below I_{cr} to a capacitance C dominated state with V_C=\sqrt{\frac{\hbar}{4eC}} \sqrt{I-I_C} above I_{cr}. The origin of the observed behavior is discussed within a single-plaquette approximation assuming the conventional RSJ model with a finite capacitance and the Ambegaokar-Baratoff relation for the critical current of the single junction.