Charge-Density-Wave Formation in the Doped Two-Leg Extended Hubbard Ladder

抄録

We investigate the electronic properties of a doped two-leg Hubbard ladder with both the onsite and nearest-neighbor Coulomb repulsions by using the weak-coupling renormalization-group method. It is shown that, for strong nearest-neighbor repulsions, the charge-density-wave state coexisting with the p-density-wave state becomes a dominant fluctuation where spins form intrachain singlets. By increasing doping rate, we have also shown that the effects of the nearest-neighbor repulsions are reduced and the system exhibits a quantum phase transition into the d-wave-like (or rung-singlet) superconducting state. We derive the effective fermion theory which describes the critical properties of the transition point with the gapless excitation of magnon. The phase diagram of the two-leg ladder compound, Sr_14−xCa_xCu₂₄O₄₁, is discussed.