The global critical current effect of superconductivity

TL;DR

This paper reveals that the critical current in superconductors can be influenced by adjacent segments, challenging traditional views and enabling new superconducting device functionalities.

Contribution

It demonstrates that the critical current is affected by measurement configuration and neighboring segments, leading to a new understanding of superconducting properties and device design.

Findings

Critical current varies with measurement configuration.

Adjacent superconducting segments can influence each other's critical current.

Superconducting diode effect can be transferred between segments.

Abstract

Superconductivity has been investigated for over a century, but there are still open questions about what determines the critical current; the maximum current a superconductor can carry before switching to its normal state. For a given superconductor, the zero-field critical current is widely believed to be determined by its inherent properties and be related to its critical magnetic field. Here, by studying superconducting polycrystalline films, single crystal flakes, and layered heterostructures, we find that the critical current of a superconductor can vary with measurement configuration. It can be influenced, or even determined, by adjacent superconducting segments along the applied current trajectory, whereas the critical magnetic field and critical temperature remain unaffected. This global critical current effect both reveals the need to revisit fundamental theory describing superconductivity, as well as implies that superconductors can transfer critical current related properties to each other. We demonstrate this by designing and fabricating a simple superconducting structure that transferred a superconducting diode effect from one segment to another segment which could not manifest the effect on its own. This observation merits a reconsideration of contemporary superconducting circuit design, and developing a full understanding will lead to a new paradigm of superconducting electronics.