Fixed-N Superconductivity: The Exact Crossover from the Bulk to the Few-Electron Limit

Fabian Braun; Jan von Delft

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Fixed-N Superconductivity: The Exact Crossover from the Bulk to the Few-Electron Limit

Fabian Braun·Jan von Delft

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Abstract

We use two truly canonical approaches to describe superconductivity in ultrasmall metallic grains: (a) a variational fixed-N projected BCS-like theory and (b) an exact solution of the model Hamiltonian developed by Richardson in context with Nuclear Physics. Thereby we obtain a description of the entire crossover from the bulk BCS regime (mean level spacing $d\ll$ bulk gap $\tildeΔ$) to the `fluctuation-dominated' few-electron regime ($d\gg\tildeΔ$). A wave-function analysis shows in detail how the BCS limit is recovered and how for $d\gg\tildeΔ$ pairing correlations become delocalized in energy space.

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BibTeX RIS

Fabian Braun, Jan von Delft. 1999-07-26. Fixed-N Superconductivity: The Exact Crossover from the Bulk to the Few-Electron Limit. https://arxiv.org/abs/cond-mat/9907402

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