Upper frequency limits for vortex guiding and ratchet effects

TL;DR

This study investigates the upper frequency limits for vortex guiding and rectification in superconducting Nb films with ferromagnetic nanostripes, revealing that guiding persists up to 2 GHz while rectification vanishes around 700 MHz, informing future high-frequency vortex control.

Contribution

The paper identifies the frequency thresholds for vortex guiding and rectification effects in nanostructured superconductors, linking them to depinning frequencies and nanostripes' geometry, advancing understanding of high-frequency vortex dynamics.

Findings

Rectified voltage vanishes at ~700 MHz

Vortex guiding persists up to ~2 GHz

Depinning frequency correlates with nanostripe geometry

Abstract

Guided and rectified motion of magnetic flux quanta are important effects governing the magneto-resistive response of nanostructured superconductors. While at low ac frequencies these effects are rather well understood, their manifestation at higher ac frequencies remains poorly investigated. Here, we explore the upper frequency limits for guided and rectified net motion of superconducting vortices in epitaxial Nb films decorated with ferromagnetic nanostripes. By combining broadband electrical spectroscopy with resistance measurements we reveal that the rectified voltage vanishes at a geometrically defined frequency of about 700 MHz. By contrast, vortex guiding-related low-ac-loss response persists up to about 2 GHz. This value corresponds to the depinning frequency $f_\mathrm{d}^\mathrm{s}$ associated with the washboard pinning potential induced by the nanostripes and exhibiting peaks for the commensurate vortex lattice configurations. Applying a sum of dc and microwave ac currents at an angle $\alpha$ with respect to the nanostripes, the angle dependence of $f_\mathrm{d}^\mathrm{s}(\alpha)$ has been found to correlate with the angle dependence of the depinning current. In all, our findings suggest that superconductors with higher $f_\mathrm{d}^\mathrm{s}$ should be favored for an efficient vortex manipulation in the GHz ac frequency range.