Dzyaloshinskii-Moriya interactions in valence bond systems

TL;DR

This paper studies how Dzyaloshinskii-Moriya interactions affect the magnetic susceptibility of valence bond systems at low temperatures, providing insights into experimental observations in kagome antiferromagnets.

Contribution

It introduces a perturbative approach to analyze Dzyaloshinskii-Moriya effects in valence bond phases, linking theory with experimental results in specific quantum spin models.

Findings

Valence bond phases remain time-reversal symmetric without magnetic field.

Susceptibility remains nonzero as temperature approaches zero.

Model explains experimental features of kagome antiferromagnets.

Abstract

We investigate the effect of Dzyaloshinskii-Moriya interactions on the low temperature magnetic susceptibility for a system whose low energy physics is dominated by short-range valence bonds (singlets). Our general perturbative approach is applied to specific models expected to be in this class, including the Shastry-Sutherland model of the spin-dimer compound SrCu_2(BO_3)_2 and the antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagome compound ZnCu_3(OH)_6Cl_2. The central result is that a short-ranged valence bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain time-reversal symmetric in the absence of a magnetic field but the susceptibility will be nonzero in the T\to 0 limit. Applied to ZnCu_3(OH)_6Cl_2, this model provides an avenue for reconciling experimental results, such as the lack of magnetic order and lack of any sign of a spin gap, with known theoretical facts about the kagome Heisenberg antiferromagnet.