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Two-gap model for underdoped cuprate superconductors

A. Perali·C. Castellani·C. Di Castro·M. Grilli·E. Piegari·A. A. Varlamov
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Abstract

Various properties of underdoped superconducting cuprates, including the momentum-dependent pseudogap opening, indicate a behavior which is neither BCS nor Bose-Einstein condensation (BEC) like. To explain this issue we introduce 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 the nodal points of the Fermi surface respectively. We find that a gap forms near the M points resulting into incoherent pairing due to strong fluctuations. Instead the pairing near the nodal points sets in with phase coherence at lower temperature. 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).

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A. Perali, C. Castellani, C. Di Castro, M. Grilli, E. Piegari, A. A. Varlamov. 2000-05-11. Two-gap model for underdoped cuprate superconductors. https://doi.org/10.1103/physrevb.62.r9295

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