Self-consistent approach to local pairing in multiorbital superconductors*

The wide morphology of  Fermi surfaces of the Iron-based superconductors, coupled with a universal relation between gap and Tc, leads us to consider a local pairing mechanism. It was shown within a mean-field theory that the interplay of large Hund’s coupling and spin-orbit coupling within the t2g orbitals of a single Iron atom leads to the local resonance of triplet states [1]. In this talk, we show that the spin symmetric, orbitally antisymmetric pre-formed pairs can escape their local environment and lead to fully gapped superconductivity in the bulk. We map this problem to a multiorbital Anderson impurity with anisotropic XXZ-like Hund’s coupling and use large-N and Schwinger boson techniques [2] to study the ground state and thermodynamic properties. We show that local Cooper pairing can be dynamically generated in this setting, and that self-consistency between the electron bath and the impurity’s degrees of freedom leads to a fully gapped triplet condensate, thus taking the tRVB theory beyond the mean-field level.

 

[1] Coleman, P., Komijani, Y., & König, E. J. (2020) Physical Review Letters, 125(7), 077001.

[2] Drouin-Touchette V, König EJ, Komijani Y, Coleman P. Physical Review B. 2021;103(20):205147