Shapiro Step at Nonequilibrium Conditions

TL;DR

This paper uses numerical simulations to study how charge imbalance affects Shapiro steps in high-temperature superconductor Josephson junctions under external radiation, revealing shifts and distribution effects.

Contribution

It introduces a detailed numerical model accounting for charge imbalance, showing its impact on Shapiro step slopes and boundary condition effects in Josephson junctions.

Findings

Charge imbalance causes a slope in Shapiro steps that increases with nonequilibrium parameters.

Coupling between junctions distributes the slope values along the stack.

Boundary conditions shift the Shapiro step position, complicating experimental interpretation.

Abstract

Detailed numerical simulations of intrinsic Josephson junctions of high temperature superconductors under external electromagnetic radiation are performed taking into account a charge imbalance effect. We demonstrate that the charge imbalance is responsible for a slope in the Shapiro step the value of which increases with a nonequilibrium parameter. Coupling between junctions leads to the distribution of the slope's values along the stack. The nonperiodic boundary conditions shift the Shapiro step in IV-characteristics from the canonical position determined by $V_{ss}=\hbar f /(2e)$, where $f$ is a frequency of external radiation. This fact makes ambiguous the interpretation of the experimentally found Shapiro step shift by the charge imbalance effect.