A Mean-Field Theory for the Spin-Gap Phase in the Two-Leg t-J Ladder

C.-Y. Mou；Y. L. Lee；Y. W. Lee；Z. Y. Weng

Chinese Journal of Physics

38卷2S期（2000 / 04 / 01）

313 - 321

英文

Two-leg t-J ladders are investigated in the framework of a combination of the phass string formulation and bond-operator representation. We develope a mean-field theory in the strong rung interaction regime, i.e. J┴ ＞＞ J, t, which provides a unified description of the undoped insulating phase and the low doping spin gap phase. The ground state of the doped phase is intrinsically a superconductor with a d-wave symmetry gap driven by the t- term. The ground-state energy is in good agreement with numerical results. Phase separation is shown to occur beyond some critical value of J/t for given doping concentration. The local structure of hole pairs as well as the spectra of various spin and charge modes are also analyzed.