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

TL;DR

This paper explores how doping affects charge-density-wave and superconducting states in a two-leg Hubbard ladder, revealing a phase transition driven by Coulomb interactions and doping levels.

Contribution

It provides a detailed analysis of the phase diagram and critical properties of the doped two-leg Hubbard ladder using renormalization-group methods.

Findings

Charge-density-wave state dominates at strong nearest-neighbor repulsions.

Doping induces a transition to a d-wave-like superconducting state.

Effective fermion theory describes the critical transition with gapless magnon excitations.

Abstract

We investigate electronic properties of the doped two-leg Hubbard ladder with both the onsite and the nearest-neighbor Coulomb repulsions, by using the 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 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-x}Ca_xCu_{24}O_{41}, is discussed.