Unconventional rf photoresponse from a superconducting spiral resonator

TL;DR

This paper demonstrates that superconducting spiral resonators with a unique current distribution can operate at higher powers with reduced nonlinear effects, enhancing their potential for rf/microwave applications.

Contribution

It introduces a novel spiral geometry that minimizes nonlinear effects in superconducting resonators, supported by experimental current distribution analysis.

Findings

Unconventional current distribution with maximum in the middle of the spiral

Reduced nonlinear effects at high rf powers due to geometry

Enhanced linearity and power handling in spiral resonators

Abstract

Superconducting thin film resonators employing strip geometries show great promise in rf/microwave applications due to their low loss and compact nature. However, their functionality is limited by nonlinear effects at elevated rf/microwave powers. Here, we show that by using a planar spiral geometry carrying parallel currents in adjacent turns, this limitation can be minimized. We investigate the rf current distributions in spiral resonators implemented with Nb thin films via laser scanning microscopy. The rf current density profile along the width of the individual turns of the resonators reveals an unconventional trend: maximum current in the middle of the structure and decaying toward its edges. This unusual behavior is associated with the circular nature of the geometry and the cancellation of magnetic field between the turns, which is favorable for handling high powers since it allows the linear characteristics to persist at high rf current densities.