Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 10: Correlated Electrons: Other Theoretical Topics

TT 10.2: Talk

Monday, March 9, 2026, 11:15–11:30, HSZ/0103

Superconductor-Insulator transition in a two-orbital attractive Hubbard model with Hund exchange — •Laura Torchia and Massimo Capone — International School for Advanced Studies (SISSA), via Bonomea 265, 34136 Trieste, Italy

We study a two-orbital attractive Hubbard model with a repulsive Hund exchange coupling J as an idealized model for a two-band superconductor. This framework is motivated by systems where a strong isotropic electron-phonon coupling drives the on-site Hubbard repulsion U negative while leaving the exchange term unaffected. We solve the model at T=0 and half-filling using DMFT, focusing on the intra-orbital singlet superconducting phase and discarding other possible instabilities, as inter-orbital pairing and a charge-density wave ordering. Already at J=0, the two-orbital model features a superconductor-insulator transition as | U| grows, in contrast with the single-orbital case which remains superconducting for any U < 0. We find that a finite J strengthens the effect of the attractive U, both in the normal state and, even more significantly, in the superconducting state. However, this pushes the system towards an effectively stronger coupling, hence to a faster transition to the insulating state.

Similarly to the Mott transition in the repulsive model, the superconductor-insulator transition here is marked by a vanishing quasi-particle weigh Z. This leads to a scenario that recalls strongly correlated superconductivity close to a Mott transition, where pairing is enhanced but phase coherence is rapidly lost, even though the present model is dominated by attractive interactions.

Keywords: Dynamical Mean-Field Theory; Strongly correlated superconductivity; Mott physics; Attractive Hubbard Model; Hund's coupling