Séminaire - Topological phase transition between the gap and the gapless superconducting states - Andrey A. Varlamov

Mercredi 14 décembre 2022 à 11 h

INSP – Barre 22-23 – 4^e étage, salle 317 – Sorbonne Université – 4 Place Jussieu – 75005 PARIS

Andrey A. Varlamov - Institute of Superconductivity and Innovative Materials (CNR-SPIN) Rome

Abstract

It is demonstrated that the quantum phase transition between the gap and gapless superconducting states in the Abrikosov-Gor'kov theory of superconducting alloy with paramagnetic impurities is of the Lifshitz type, i.e. of the  order. This phase transition has a topological nature and is characterized by the corresponding change of the topological invariant, namely the Euler characteristic. We study the stability of such a transition with respect to the spatial fluctuations of the magnetic impurities critical concentration  and show that the requirement for validity of its mean field description is unobtrusive: (here  is the superconducting coherence length).  Finally, we show that, similarly to the Lifshitz point, the   order phase transition should be accompanied by the corresponding singularities, for instance, the superconducting thermoelectric effect has a giant peak exceeding the normal value of the Seebeck coefficient by the ratio of the Fermi energy and the superconducting gap.