Probing the limits of superconductivity

TL;DR

This paper challenges the common interpretation of superconducting phase transitions based on scaling analysis, showing that such data may not conclusively prove zero resistance and suggesting the persistence of small resistance at low temperatures.

Contribution

It identifies limitations of the scaling function approach in analyzing superconductivity data and proposes a criterion to validate such analyses.

Findings

Scaling collapse occurs over a wide parameter range, questioning its significance.

Literature data fail the proposed validity criterion.

Evidence suggests small but non-zero resistance persists at low temperatures.

Abstract

DC voltage versus current measurements of superconductors in a magnetic field are widely interpreted to imply that a phase transition occurs into a state of zero resistance. We show that the widely-used scaling function approach has a problem: Good data collapse occurs for a wide range of critical exponents and temperatures. This strongly suggests that agreement with scaling alone does not prove the existence of the phase transition. We discuss a criterion to determine if the scaling analysis is valid, and find that all of the data in the literature that we have analyzed fail to meet this criterion. Our data on YBCO films, and other data that we have analyzed, are more consistent with the occurrence of small but non-zero resistance at low temperature.