Thermodynamics of small superconductors with fixed particle number

TL;DR

This paper applies the Variation After Projection method to the pairing Hamiltonian to accurately describe the thermodynamics of small superconducting systems with fixed particle number across all temperature ranges.

Contribution

It introduces the first application of Variation After Projection at finite temperature to the pairing Hamiltonian for small systems with fixed particle number.

Findings

Accurately reproduces exact canonical properties at all temperatures

Effective for both odd and even particle systems

Provides a reliable method for small superconductor thermodynamics

Abstract

The Variation After Projection approach is applied for the first time to the pairing hamiltonian to describe the thermodynamics of small systems with fixed particle number. The minimization of the free energy is made by a direct diagonalization of the entropy. The Variation After Projection applied at finite temperature provides a perfect reproduction of the exact canonical properties of odd or even systems from very low to high temperature.