Magnetization Plateaux in Random Frustrated S=1/2 Heisenberg Chains

TL;DR

This paper investigates how randomness affects magnetization plateaux in frustrated S=1/2 Heisenberg chains, revealing that certain plateaux vanish or shift, with new fractional plateaux emerging due to disorder.

Contribution

It provides a detailed analysis of the impact of randomness on magnetization plateaux in frustrated chains, including the disappearance, shifting, and emergence of new plateaux, which was not previously understood.

Findings

The $ ext{M}_s/2$ plateau vanishes immediately with randomness.

A small plateau appears near saturation due to localized spins.

Random ferromagnetic bonds induce fractional plateaux and cause splitting of existing ones.

Abstract

The $S=1/2$ frustrated Heisenberg chains with bond alternation is known to exhibit a magnetization plateau at half of the saturation magnetization $\Ms$ accompanied by the spontanuous translational symmetry breakdown. The effect of randomness on the magnetization process of this model is investigated. First we consider the mixture of the two kinds of chains both of which possess the $\Ms/2$-plateau in the common interval of the magnetization field. The plateau at $\Ms/2$ is found to vanish immediately if the randomness is switched on in agreement with Totsuka's prediction. The small plateau also appears near the saturation field due to the localization of inverted spins around the minority bond. On the other hand, if the stronger bond is replaced by the ferromagnetic bonds randomly, the randomness induced fractional plateau appears as in the nonfrustrated case. The plateau at $\Ms/2$ does not simply vanish but shifts and splits into two smaller plateaux. The magnetization on this plateau varies nonlinearly with $1-p$. The physical origin of this behavior is explained based on the strong coupling picture.