Tuning current flow in superconducting thin film strips by control wires. Applications to single photon detectors and diodes

TL;DR

This paper demonstrates how integrating control wires with superconducting thin films can engineer supercurrent profiles, reduce vortex penetration, and enable tunable, wide-area single-photon detectors and superconducting diodes.

Contribution

It introduces a method to control supercurrent distribution in thin films using control wires, enhancing detector performance and diode behavior.

Findings

Engineered supercurrent profiles without edge crowding.

Tuned supercurrent profiles to mitigate vortex entry.

Proposed wide, tunable single-photon detectors and diodes.

Abstract

It is shown that integration of a thin film superconducting strip with current-carrying control wires enables one to engineer a profile of supercurrent density $J(x)$ with no current crowding at the edges of a strip wider than the magnetic Pearl length $\Lambda$. Moreover, $J(x)$ in a strip can be tuned by control wires to produce an inverted $J(x)$ profile with dips at the edges to mitigate current crowding at lithographic defects and block premature penetration of vortices. These conclusions are corroborated by calculations of $J(x)$ in a thin strip coupled inductively with side control wires or in bilayer strip structures by solving the London and Ginzburg Landau equations in the thin film Pearl limit. Thermally-activated penetration of vortices from the edges and unbinding of vortex-antivortex pairs in inverted $J(x)$ profiles are evaluated. It is shown that these structures can be used to develop single-photon strip detectors much wider than $\Lambda$. Such detectors can be tuned {\it in situ} by varying current in control wires to reach the ultimate photon sensitivity limited by unbinding of vortex-antivortex pairs. The structures considered here exhibit a non-reciprocal current response and behave as superconducting diodes. They can also be used to study the physics of vortex matter in thin films not masked by penetration of vortices from the edges.