On the dimerized phase in the cross-coupled antiferromagnetic spin ladder

TL;DR

This paper critically reexamines the existence of a dimerized phase in a frustrated spin ladder model, using advanced numerical methods to set tighter limits on its possible presence.

Contribution

It provides a more careful numerical analysis that challenges previous claims of a columnar dimer phase in the model.

Findings

Previous evidence for the dimerized phase is not conclusive.

Tighter bounds on the dimer order parameter are established.

The existence of the dimerized phase cannot be definitively confirmed or ruled out.

Abstract

We revisit the phase diagram of the frustrated s=1/2 spin ladder with antiferromagnetic rung and diagonal couplings. In particular, we reexamine the evidence for the columnar dimer phase, which has been predicted from analytic treatment of the model and has been claimed to be found in numerical calculations. By considering longer chains and by keeping more states than in previous work using the density-matrix renormalization group, we show that the numerical evidence presented previously for the existence of the dimerized phase is not unambiguous in view of the present more careful analysis. While we cannot completely rule out the possibility of a dimerized phase in the cross-coupled ladder, we do set limits on the maximum possible value of the dimer order parameter that are much smaller than those found previously.