Microwave response of a metallic superconductor subject to a high-voltage gate electrode

TL;DR

This study investigates how a high-voltage gate electrode influences a metallic superconductor's microwave response, aiming to understand the electric field effects and their implications for superconductor theory and applications.

Contribution

It provides experimental insights into the electric-field response of superconductors, challenging existing theories and informing future technological developments.

Findings

Superconductor characteristics change with applied gate voltage.

Leakage currents affect the superconductor's impedance.

Temperature variations influence the observed effects.

Abstract

Processes that lead to the critical-current suppression and change of impedance of a superconductor under the application of an external voltage is an active area of research, especially due to various possible technological applications. In particular, field-effect transistors and radiation detectors have been developed in the recent years, showing the potential for precision and sensitivity exceeding their normal-metal counterparts. In order to describe the phenomenon that leads to the critical-current suppression in metallic superconducting structures, a field-effect hypothesis has been formulated, stating that an electric field can penetrate the metallic superconductor and affect its characteristics. The existence of such an effect would imply the incompleteness of the underlying theory, and hence indicate an important gap in the general comprehension of superconductors. In addition to its theoretical value, a complete understanding of the phenomenon underneath the electric-field response of the superconductor is important in the light of the related technological applications. In this paper, we study the change of the characteristics of a superconductor implementing a coplanar-waveguide resonator as a tank circuit, by relating our measurements to the reactance and resistance of the material. Namely, we track the state of the superconductor at different voltages and resulting leakage currents of a nearby gate electrode which is not galvanically connected to the resonator. By comparing the effects of the leakage current and of a change in the temperature of the system, we conclude that the observed behaviour in the superconductor is [...]