Dresden 2020 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 14: Superconductivity: Theory 1

TT 14.10: Vortrag

Montag, 16. März 2020, 17:45–18:00, HSZ 204

Eliashberg equations for an electron-phonon version of the Sachdev-Ye-Kitaev model: Pair Breaking in non-Fermi liquid superconductors — •Daniel Hauck1, Markus Klug1, Ilya Esterlis2, and Jörg Schmalian1,31Institute for Theory of Condensed Matter, Karlsruhe Institute of Technology, Karlsruhe 76131, Germany — 2Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA — 3Institute for Solid State Physics, Karlsruhe Institute of Technology, Karlsruhe 76021, Germany

We present a theory that is a non-Fermi-liquid counterpart of the Abrikosov-Gor’kov pair-breaking theory due to paramagnetic impurities in superconductors. To this end we analyze a model of interacting electrons and phonons that is a natural generalization of the Sachdev-Ye-Kitaev-model. In the limit of large numbers of degrees of freedom, the Eliashberg equations of superconductivity become exact and emerge as saddle-point equations of a field theory with fluctuating pairing fields. In its normal state the model is governed by two non-Fermi liquid fixed points, characterized by distinct universal exponents. At low temperatures a superconducting state emerges from the critical normal state. We study the role of pair-breaking on Tc, where we allow for disorder that breaks time-reversal symmetry. For small Bogoliubov quasi-particle weight, relevant for systems with strongly incoherent normal state, Tc drops rapidly as function of the pair breaking strength before it vanishes at a critical pair-breaking strength via an essential singularity. The latter signals a breakdown of the emergent conformal symmetry of the non-Fermi liquid normal state.

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