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Superconductivity on the honeycomb lattice: Semimetal-to-superconductor transition and BCS-BEC crossover | | Erhai Zhao
; Arun Paramekanti
; | | Date: |
18 Jun 2006 | | Subject: | Superconductivity; Strongly Correlated Electrons | | Abstract: | We study the attractive Hubbard model on the two-dimensional honeycomb lattice, focusing on the semimetal-to-superconductor transition at half-filling (at a critical interaction strength $U_c$) and the BCS-to-BEC crossover for small deviations from half-filling. At a small density deviation $delta n$ from half-filling, we find that although the underlying metallic state has a small Fermi surface and a small effective Fermi energy $sim v_F sqrt{delta n}$, the BCS-to-BEC crossover occurs at an interaction strength $U sim U_c gg v_F sqrt{delta n}$ and involves all the fermions in the underlying semimetal. The crossover regime and the maximum SC transition temperature thus occur close to the quantum critical point at half-filling. We compute the SC collective modes spectra in the crossover regime and show that an undamped Leggett mode emerges deep in the BEC regime in addition to the Goldstone sound mode. In the semimetal phase, the long wavelength SC fluctuations are critically damped by the gapless Dirac fermions while short wavelength fluctuations can propagate as weakly damped excitations. | | Source: | arXiv, cond-mat/0606470 | | Services: | Forum | Review | PDF | Favorites | |
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