BCS to Bose-Einstein crossover phase diagram at zero temperature for a dx2−y2 order parameter superconductor: Dependence on the tight-binding structure

Abstract

We study the effect of the next-nearest-neighbor (NNN) hopping matrix element t′ on the zero-temperature (T=0K) crossover phase diagram, namely, from the BCS limit to the Bose-Einstein regime, for a model which presents a dx2−y2 superconductor order parameter symmetry. This theoretical generalization is required by angle-resolved photoemission spectroscopy experiments. Our NNN hopping is characterized by the parameter α≡t′/t≠0, where t is the nearest neighbor hopping matrix element. For α⩾0, there is a crossover of BCS binding energy type as described [B. C. den Hertog, Phys. Rev. B 60, 559 (1999)] by keeping the density fixed. However, for α<0, the system is always in the Bose-Einstein regime for n<~nc≈0.12. We conclude that the presence of the NNN hopping matrix element drastically influences the crossover diagram for a dx2−y2 superconductor.

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