Observation of the Non-linear Meissner Effect

Abstract

A long-standing theoretical prediction is that in clean, nodal unconventional superconductors the magnetic penetration depth $\lambda$, 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 $\lambda$, 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 $\lambda (T)$ 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.

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Cited by in corpus (3)

• Nonlocal electrodynamics and the penetration depth of superconducting Sr${}_2$RuO${}_4$
• Impurity strength-temperature phase diagram with phase crystals and competing time-reversal symmetry breaking states in nodal $d$-wave superconductors
• Hund's coupling assisted orbital-selective superconductivity in Ba1-xKxFe2As2