Attempts to test an alternative electrodynamic theory of superconductors by low-temperature scanning tunneling and atomic force microscopy

TL;DR

This study tests an alternative electrodynamic theory of superconductors against the standard London theory by attempting to detect differences in electric field screening using atomic force microscopy, but limited accuracy prevents definitive conclusions.

Contribution

The paper conducts an experimental comparison of two superconducting electrodynamics theories using advanced microscopy techniques, providing empirical data to evaluate their differences.

Findings

No detectable difference in electric field screening within measurement accuracy

Superconductive transition does not alter atomic-scale tip-sample interactions

Limited measurement precision prevents confirming or refuting Hirsch's hypothesis

Abstract

We perform an experiment to test between two theories of the electrodynamics of superconductors: the standard London theory and an alternative proposed by J. E. Hirsch [Phys. Rev. B 69, 214515 (2004)]. The two alternatives give different predictions with respect to the screening of an electric field by a superconductor, and we try to detect this effect using atomic force microscopy on a niobium sample. We also perform the reverse experiment, where we demonstrate a superconductive tip mounted on a qPlus force sensor. Due to limited accuracy, we are able neither to prove nor to disprove Hirsch's hypothesis. Within our accuracy of 0.17 N/m, the superconductive transition does not alter the atomic-scale interaction between tip and sample.