Dual cut-off dc-tunable microwave low-pass filter on superconducting Nb microstrips with asymmetric nanogrooves

TL;DR

This paper introduces a superconducting Nb microstrip low-pass microwave filter with asymmetric nanogrooves, whose cut-off frequency can be dc-tuned by manipulating vortex pinning, enhancing microwave loss control in superconducting circuits.

Contribution

It demonstrates a novel dc-tunable low-pass filter based on asymmetric nanogrooves that modulate vortex dynamics to control microwave frequency response.

Findings

The filter's cut-off frequency is tunable via dc bias.

Microwave loss is minimized when vortex lattice matches nanogrooves.

The device operates through a crossover in vortex dissipation regimes.

Abstract

We present a dual cut-off, dc-tunable low-pass microwave filter on a superconducting Nb microstrip with uniaxial asymmetric nanogrooves. The frequency response of the device was measured in the range $300$\,KHz to $14$\,GHz at different temperatures, magnetic fields, and dc current values. The microwave loss is most effectively reduced when the Abrikosov vortex lattice spatially matches the underlying washboard pinning landscape. The forward transmission coefficient $S_{21}(f)$ of the microstrip has a dc-tunable cut-off frequency $f_d$ which notably changes under dc bias reversal, due to the two different slope steepnesses of the pinning landscape. The device's operation principle relies upon a crossover from the weakly dissipative response of vortices at low frequencies when they are driven over the grooves, to the strongly dissipative response at high frequencies when the vortices are oscillating within one groove. The filter's cut-off frequency is the vortex depinning frequency tunable by the dc bias as it diminishes the pinning effect induced by the nanopattern. The reported results unveil an advanced microwave functionality of superconducting films with asymmetric (ratchet) pinning landscapes and are relevant for tuning the microwave loss in superconducting planar transmission lines.