20.07.23: Special Condensed Matter Theory Seminar by Prof. Tai Kai Ng on A theoretical journey towards the anomalous metal state

Arbeitsgruppenleiter Quantenfeldtheorie für korrelierte Vielteilchensysteme Universität Hamburg Fakultät für Mathematik, Informatik und Naturwissenschaften

20.07.2023 at 09:00 

Motivated by the discovery of the anomalous metal state in superconductor thin films, I shall present results of two studies by my group in this talk: (i) A model of mixed metallic and superconducting grains coupled by electron tunneling - the metallic grains are expected to become superconducting because of proximity effect in a mean-field treatment of the model. We show that when quantum fluctuations in relative phases between different grains are taken into account, the proximity effect can be destroyed and the metallic and superconducting grains become "insulating" with respect to each other when the charging energy between grains are strong enough and tunneling between grains are weak enough [1]; and (ii) We apply the replica trick to study a model of dirty metals with net attractive interactions. Within a replica-symmetric BCS mean field theory, we show that there is a superconductor to superconductor-glass transition beyond a critical strength of disorder. The spectral gap in single particle density of states is widened strongly by disorder and the superfluid density decreases rapidly with increasing strength of disorder but does not vanish completely in the superconductor-glass state. The finite frequency responses are computed and the nature of the low-energy excitation spectrum is discussed. The relevance of our result to the anomalous metal state is discussed. [1] TK Ng, "Proximity effect and Anomalous metal state in a model of mixed metal-superconductor grains" arXiv:2305.15763