Abstract
A superconductor/normal metal/superconductor Josephson junction is a coherent electron system where the thermodynamic entropy depends on temperature and difference of phase across the weak-link. Here, exploiting the phase-temperature thermodynamic diagram of a thermally isolated system, we argue that a cooling effect can be achieved when the phase drop across the junction is brought from 0 to π in a iso-entropic process. We show that iso-entropic cooling can be enhanced with proper choice of geometrical and electrical parameters of the junction, i.e. by increasing the ratio between supercurrent and total junction volume. We present extensive numerical calculations using quasi-classical Green function methods for a short junction and we compare them with analytical results. Interestingly, we demonstrate that phase-coherent thermodynamic cycles can be implemented by combining iso-entropic and iso-phasic processes acting on the weak-link, thereby engineering the coherent version of thermal machines such as engines and cooling systems. We therefore evaluate their performances and the minimum temperature achievable in a cooling cycle.
Highlights
From SINIS structures, here the mechanism relies on proximity effect[39,40,41], which takes place when a normal metal is in good electric contact with a superconductor
We have considered the thermodynamic properties of a proximized SNS Josephson junction in the diffusive regime
We have shown that the phase- and temperature-dependent entropy can be exploited to achieve significant temperature decrease of the electronic degrees of freedom of the system
Summary
Francesco Vischi[1,2], Matteo Carrega[1], Pauli Virtanen[1], Elia Strambini[1], Alessandro Braggio1 & Francesco Giazotto[1]. From SINIS structures, here the mechanism relies on proximity effect[39,40,41], which takes place when a normal metal is in good electric contact with a superconductor This allows to develop a phase-tunable minigap in the quasi-particle Density of States (DoS) of the normal region[42,43,44,45], when the weak-link is shorter or comparable to the superconducting coherence length ξ. This results in a non-trivial phase dependence of thermodynamic quantities, such as the entropy or the specific heat of the SNS junction.
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