The superconducting gap in the Hubbard model and the two gap energy scales in high-Tc cuprates

摘要

Recent excperiments (ARPES, Raman) suggest the presence of two distinctenergy gaps in high-Tc superconductors (HTSC), exhibiting different dopingdependences. Results of a variational cluster approach to the superconductingstate of the two-dimensional Hubbard model are presented which show that thismodel qualitatively describes this gap dichotomy: One gap (antinodal) increaseswith less doping, a behavior long considered as reflecting the general gapbehavior of the HTSC. On the other hand, the near-nodal gap does even slightlydecrease with underdoping. An explanation of this unexpected behavior is givenwhich emphasizes the crucial role of spin fluctuations in the pairingmechanism.