Anisotropic second-harmonic generation in superconducting nanostructures

TL;DR

This paper investigates how noncollinear magnetic field configurations induce anisotropic second-harmonic generation in superconducting nanostructures, revealing a new nonlinear response mechanism relevant for quantum device applications.

Contribution

It extends the analysis of nonlinear electrodynamics in superconducting nanostructures to noncollinear magnetic fields, demonstrating a dominant second-harmonic response from Meissner-current saturation.

Findings

Second-harmonic response is enhanced in noncollinear configurations.

Anisotropic second-harmonic signals are directionally separated from first-harmonic components.

Response originates from Meissner-current saturation and nonlinear oscillations.

Abstract

Circuits based on superconducting nanostructures are among the most promising platforms for quantum computing. Understanding how device geometry governs nonlinear electrodynamics is crucial for implementing superconducting quantum technologies. However, to date, research has largely been limited to superconducting nanostructures with collinearly aligned static and dynamic applied magnetic fields. Here, we analyze the dynamics of Meissner currents and Abrikosov vortices in a superconducting nanocube exposed to combined static and microwave magnetic fields, extending the analysis to a more general excitation geometry. We demonstrate that, in a noncollinear configuration,the magnetization component parallel to the static field develops a dominant second-harmonic response under the microwave driving. This effect is strongly enhanced when Meissner currents saturate at static fields just below the thresholds for successive vortex nucleation. By numerically solving the time-dependent Ginzburg-Landau equations, we show that the response originates from Meissner-current saturation combined with the nonlinear oscillations of normal-phase indentations, yielding an anisotropic second-harmonic signal that is directionally separated from, and not overshadowed by, the first-harmonic component of the dynamic magnetization. These findings are relevant for superconducting devices that require controllable high-frequency nonlinearity.