Frequency dispersion of nonlinear response of thin superconducting films in Berezinskii-Kosterlitz-Thouless state

TL;DR

This study investigates how microwave radiation affects the nonlinear transport properties of thin superconducting films near the Berezinskii-Kosterlitz-Thouless transition, revealing a high-frequency cutoff where nonlinear response diminishes.

Contribution

It provides experimental and numerical analysis of the frequency-dependent nonlinear response of 2D superconducting films, highlighting a cutoff frequency and the suppression of vortex-antivortex dissociation at high frequencies.

Findings

Nonlinear response decreases significantly above ~2 GHz

Numerical simulations match low-frequency behavior but not high-frequency

High-frequency oscillations suppress vortex-antivortex dissociation

Abstract

The effects of microwave radiation on the transport properties of atomically thin $La_{2-x}Sr_xCuO_4$ films were studied in the 0.1-13 GHz frequency range. Resistance changes induced by microwaves were investigated at different temperatures near the superconducting transition. The nonlinear response decreases by several orders of magnitude within a few GHz of a cutoff frequency $\nu_{cut} \approx$ 2 GHz. Numerical simulations that assume an ac response to follow the dc V-I characteristics of the films reproduce well the low frequency behavior, but fail above $\nu_{cut}$. The results indicate that two-dimensional superconductivity is resilient against high-frequency microwave radiation, because vortex-antivortex dissociation is dramatically suppressed in two-dimensional superconducting condensates oscillating at high frequencies.