Thermodynamic transition of small superconducting particles

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Abstract
Measurements are presented which show that the specific heat of small tin particles exhibits a BCS-like structure at the superconducting transition even if the particle size is much smaller than the superconducting coherence length. This structure remains, broadened by fluctuation effects, down to dimensions so small that size quantization produces an electronic energy level spacing larger than the superconducting energy gap. Our results suggest that this energy ratio determines the crossover from bulk behavior (with a well-defined phase transition) to zero-dimensional behavior (with no superconducting order).