Superconductor-Insulator transition in a two-orbital attractive Hubbard model with Hund's exchange
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866914293957525504 |
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| author | Torchia, Laura Capone, Massimo |
| author_facet | Torchia, Laura Capone, Massimo |
| contents | We study a two-orbital attractive Hubbard model with a repulsive Hund's exchange coupling $J$ as an idealized model for a two-band superconductor. This framework is motivated by a system where a large isotropic electron-phonon coupling drives the on-site Hubbard repulsion $U$ negative, while leaving the exchange term unaffected. We focus on the intra-orbital (intra-band) singlet superconducting phase and we solve the model at zero temperature and half-filling using Dynamical Mean-Field Theory. Already at $J=0$, the two-orbital model features a superconductor-insulator transition as $\vert U\vert$ grows, as opposed to 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, 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.
Remarkably, the transition from a superconductor to an insulator occurs with a vanishing quasi-particle weight $Z$ and in a scenario that recalls strongly correlated superconductivity close to a Mott transition, even though the present model is dominated by attractive interactions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_08597 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Superconductor-Insulator transition in a two-orbital attractive Hubbard model with Hund's exchange Torchia, Laura Capone, Massimo Strongly Correlated Electrons Superconductivity We study a two-orbital attractive Hubbard model with a repulsive Hund's exchange coupling $J$ as an idealized model for a two-band superconductor. This framework is motivated by a system where a large isotropic electron-phonon coupling drives the on-site Hubbard repulsion $U$ negative, while leaving the exchange term unaffected. We focus on the intra-orbital (intra-band) singlet superconducting phase and we solve the model at zero temperature and half-filling using Dynamical Mean-Field Theory. Already at $J=0$, the two-orbital model features a superconductor-insulator transition as $\vert U\vert$ grows, as opposed to 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, 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. Remarkably, the transition from a superconductor to an insulator occurs with a vanishing quasi-particle weight $Z$ and in a scenario that recalls strongly correlated superconductivity close to a Mott transition, even though the present model is dominated by attractive interactions. |
| title | Superconductor-Insulator transition in a two-orbital attractive Hubbard model with Hund's exchange |
| topic | Strongly Correlated Electrons Superconductivity |
| url | https://arxiv.org/abs/2505.08597 |