Nonlinear sigma model study of a frustrated spin ladder

TL;DR

This paper investigates a frustrated two-leg spin ladder model using the nonlinear sigma model, revealing a complex phase diagram with multiple gapless phases and topologically distinct Haldane-type phases, especially for spin-1/2 systems.

Contribution

It introduces a nonlinear sigma model analysis of a frustrated spin ladder, identifying new phase boundaries and topological distinctions not previously characterized.

Findings

Multiple gapless phase boundaries identified.

Topologically distinct Haldane-type phases characterized.

Phase diagram shows rich structure with frustration effects.

Abstract

A model of two-leg spin-S ladder with two additional frustrating diagonal exchange couplings J_{D}, J_{D}' is studied within the framework of the nonlinear sigma model approach. The phase diagram has a rich structure and contains 2S gapless phase boundaries which split off the boundary to the fully saturated ferromagnetic phase when J_{D} and J_{D}' become different. For the S=1/2 case, the phase boundaries are identified as separating two topologically distinct Haldane-type phases discussed recently by Kim et al. (cond-mat/9910023).