Thermodynamic properties of a small superconducting grain
Thermodynamic properties of a small superconducting grain
The reduced BCS Hamiltonian for a metallic grain with a finite number of electrons is considered. The crossover between the ultrasmall regime, in which the level spacing d is larger than the bulk superconducting gap $\ensuremath{\Delta}$ and the small regime, where $\ensuremath{\Delta}\ensuremath{\gtrsim}d,$ is investigated analytically and numerically. The condensation energy, …