Recently, Matsukawa et al. have discovered a new superconductor, Pr_2Ba_4Cu_7O_<15-δ>, in which metallic CuO double chains are responsible for the superconductivity. To investigate its superconductivity, we employ the d-p double chain model where the tight-binding parameters are determined so as to fit a band structure in the local density approximation (LDA). On the basis of the Tomonaga-Luttinger liquid theory, we obtain a phase diagram that includes the superconducting phase in the weak coupling limit. We also calculate the Luttinger liquid parameter K_ρ as a function of the electron density n using the Hartree-Fock approximation. With increasing n from quarter filling, K_ρ increases and then exceeds 1/2 when the superconducting correlation becomes most dominant. K_ρ has a maximum at an optimal density between quarter- and half-filling. These results are consistent with the experimental observation.
Superconductivity in the CuO double chain of Pr_2Ba_4Cu_7O_<15-δ> on the basis of Tomonaga-Luttinger liquid Theory
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