Paramagnetic Breakdown of Superconductivity in Ultrasmall Metallic Grains
نویسندگان
چکیده
We study the magnetic-field-induced breakdown of superconductivity in nm-scale metal grains having a mean electron level spacing d . D̃ (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 firstorder transition observed for the latter can be made continuous by finite size effects. The meanfield procedure of describing the system by a single pairing parameter D breaks down for d . D̃. [S0031-9007(97)03675-2]
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