Observation of the Non-linear Meissner Effect

J. A. Wilcox; M. J. Grant; L. Malone; C. Putzke; D. Kaczorowski; T. Wolf; F. Hardy; C. Meingast; J. G. Analytis; J. -H. Chu; I. R. Fisher; A. Carrington

doi:10.1038/s41467-022-28790-y

paper

Observation of the Non-linear Meissner Effect

arXiv:2008.04050 · doi:10.1038/s41467-022-28790-y

Abstract

A long-standing theoretical prediction is that in clean, nodal unconventional superconductors the magnetic penetration depth $λ$ , at zero temperature, varies linearly with magnetic field. This non-linear Meissner effect is an equally important manifestation of the nodal state as the well studied linear-in- $T$ dependence of $λ$ , but has never been convincingly experimentally observed. Here we present measurements of the nodal superconductors CeCoIn $_{5}$ and LaFePO which clearly show this non-linear Meissner effect. We further show how the effect of a small dc magnetic field on $λ (T)$ can be used to distinguish gap nodes from non-nodal deep gap minima. Our measurements of KFe $_{2}$ As $_{2}$ suggest that this material has such a non-nodal state.