Two-gap model for underdoped cuprate superconductors
Abstract
Various properties of underdoped superconducting cuprates, including the momentum dependent pseudogap opening, indicate a mixed BCS vs Bose-Einstein behavior, which we describe in terms of a two-gap model. This model assumes an anisotropic pairing interaction among two kinds of fermions with small and large Fermi velocities representing the quasiparticles near the M and nodal points of the Fermi surface respectively. By evaluating the superconducting fluctuation propagator, we find that the gap near the M points experiences strong short wave-length fluctuations below the mean-field pairing temperature until phase coherence is established by coupling to the stiffness of the pairing near the nodal points. By tuning the momentum dependent interaction, the model allows for a continuous evolution from a pure BCS pairing (in the overdoped and optimally doped regime) to a mixed boson-fermion picture (in the strongly underdoped regime).Keywords
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