Superconductivity in the CuO double chain of Pr₂Ba₄Cu₇O₁5-delta on the basis of Tomonaga-Luttinger liquid theory

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Recently, Matsukawa et al. have discovered a new superconductor Pr₂Ba₄Cu₇O₁5-delta in which metallic CuO double chains are responsible for the superconductivity. To investigate the superconductivity, we employ the d-p double chain model where the tight-binding parameters are determined so as to fit the LDA band structure. On the basis of the Tomonaga-Luttinger liquid theory, we obtain the phase diagram including the superconducting phase in the weak coupling limit. We also calculate the Luttinger liquid parameter Kᵣho as a function of the electron density n by using the Hartree-Fock approximation. With increasing n from quarter filling, Kᵣho increases, and then exceeds 1/2 when the superconducting correlation becomes most dominant. Kᵣho has a maximum at an optimal density between quarter- and half-filling. These results are consistent with the experimental observation.