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

Recently, Matsukawa et al. discovered a new superconductor, Pr2Ba4Cu7O15-delta, 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-p as a function of the electron density n using the Hartree-Fock approximation. With increasing n from quarter filling, K-p increases and then exceeds 1/2 when the superconducting correlation becomes most dominant. K-p has a maximum at an optimal density between quarter- and half-filling. These results are consistent with the experimental observation.