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Paramagnetic Breakdown of Superconductivity in Ultrasmall Metallic Grains

Fabian Braun·Jan von Delft·D. C. Ralph·M. Tinkham
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Abstract

We study the magnetic-field-induced breakdown of superconductivity in nm-scale metal grains having a mean electron level spacing $d \simeq \tildeΔ$ (bulk gap). Using a generalized variational BCS approach that yields good qualitative agreement with measured spectra, we argue that Pauli paramagnetism dominates orbital diamagnetism, as in the case of thin films in a parallel magnetic field. However, the first-order transition observed for the latter can be made continuous by finite size effects. The mean-field procedure of describing the system by a single pairing parameter $Δ$ breaks down for $d \simeq \tildeΔ$.

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Fabian Braun, Jan von Delft, D. C. Ralph, M. Tinkham. 1997-07-31. Paramagnetic Breakdown of Superconductivity in Ultrasmall Metallic Grains. https://doi.org/10.1103/physrevlett.79.921

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