Condensation of magnons and spinons in a frustrated ladder

TL;DR

This paper provides a detailed theoretical analysis of a frustrated quantum spin ladder in a magnetic field, revealing complex magnetization behavior and the effects of anisotropic interactions, supported by analytical and numerical methods.

Contribution

It introduces a comprehensive theoretical framework for understanding magnetization plateaux and excitations in a frustrated ladder, highlighting the impact of anisotropic interactions.

Findings

Magnetization curve exhibits complex behavior explained by elementary excitations.

Anisotropic interactions open a gap between plateaux, which closes at fractional plateaux.

Density Matrix Renormalization Group calculations support analytical results.

Abstract

Motivated by the ever-increasing experimental effort devoted to the properties of frustrated quantum magnets in a magnetic field, we present a careful and detailed theoretical analysis of a one-dimensional version of this problem, a frustrated ladder with a magnetization plateau at m=1/2. We show that even for purely isotropic Heisenberg interactions, the magnetization curve exhibits a rather complex behavior that can be fully accounted for in terms of simple elementary excitations. The introduction of anisotropic interactions (e.g., Dzyaloshinskii-Moriya interactions) modifies significantly the picture and reveals an essential difference between integer and fractional plateaux. In particular, anisotropic interactions generically open a gap in the region between the plateaux, but we show that this gap closes upon entering fractional plateaux. All of these conclusions, based on analytical arguments, are supported by extensive Density Matrix Renormalization Group calculations.