We consider a model of spin-gapped chains weakly coupled by Josephson and Coulomb interactions. Combining such nonperturbative methods as bosonization and the Bethe ansatz to treat the intrachain interactions with the random phase approximation for the interchain couplings and the first corrections to this, we investigate the phase diagram of this model. The phase diagram shows both charge-density wave ordering and superconductivity. These phases are separated by line of critical points which exhibits an approximate SU(2) symmetry. We consider the effects of a magnetic field on the system. We apply the theory to the material ${\mathrm{Sr}}_2{\mathrm{Ca}}_{12}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ and suggest further experiments.

• Received 14 November 2001

DOI:https://doi.org/10.1103/PhysRevB.65.195121