Hidden fermionic excitation in the superconductivity of the strongly attractive Hubbard model

Abstract

We scrutinize the real-frequency structure of the self-energy in the superconducting state of the attractive Hubbard model within the dynamical mean-field theory. Within the strong-coupling superconducting phase which has been understood in terms of the Bose-Einstein condensation in the literature, we find two qualitatively different regions crossing over each other. In one region close to zero temperature, the self-energy depends on the frequency only weakly at low energy. On the other hand, in the region close to the critical temperature, the self-energy shows a pole structure. The latter region becomes more dominant as the interaction becomes stronger. We reveal that the self-energy pole in the latter region is generated by a coupling to a hidden fermionic excitation. The hidden fermion persists in the normal state, where it yields a pseudogap. We compare these properties with those of the repulsive Hubbard model relevant for high-temperature cuprate superconductors, showing that hidden fermions are a key common ingredient in strongly correlated superconductivity.

7 pages, 7 figures (including supplementary information)

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• Antagonistic effects of nearest-neighbor repulsion on the superconducting pairing dynamics in the doped Mott insulator regime
• Direct Connection between Mott Insulator and d-Wave High-Temperature Superconductor Revealed by Continuous Evolution of Self-Energy Poles
• Unconventional Pairing from Local Orbital Fluctuations in Strongly Correlated A${}_3$C${}_{60}$
• Brillouin-zone integration scheme for many-body density of states: Tetrahedron method combined with cluster perturbation theory
• Strong-coupling high-$T_{\mathrm{c}}$ superconductivity in doped correlated band insulators
• Hidden Bose-Einstein Singularities in Correlated Electron Systems
• Hidden Bose-Einstein Singularities in Correlated Electron Systems: II. Pseudogap Phase in the Weakly Attractive Hubbard Model
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