Phase diagram of the three band half-filled Cu-O two-leg ladder

TL;DR

This paper maps the phase diagram of a half-filled two-leg Cu-O ladder considering both weak and strong coupling regimes, revealing different phases depending on orbital inclusion and coupling strength.

Contribution

It provides a comprehensive analysis of the phase diagram including effects of outer oxygen orbitals and compares weak and strong coupling results.

Findings

D-Mott phase appears without outer oxygen orbitals

Dimerized phase emerges with outer oxygen orbitals

Circulating current phase does not occur at weak coupling

Abstract

We determine the phase diagram of the half-filled two-leg ladder both at weak and strong coupling, taking into account the Cu d_{x^2-y^2} and the O p_x and p_y orbitals. At weak coupling, renormalization group flows are interpreted with the use of bosonization. Two different models with and without outer oxygen orbitals are examined. For physical parameters, and in the absence of the outer oxygen orbitals, the D-Mott phase arises; a dimerized phase appears when the outer oxygen atoms are included. We show that the circulating current phase that preserves translational symmetry does not appear at weak coupling. In the opposite strong-coupling atomic limit the model is purely electrostatic and the ground states may be found by simple energy minimization. The phase diagram so obtained is compared to the weak-coupling one.