Spin Waves in Random Spin Chains

TL;DR

This paper investigates the effects of random antiferromagnetic impurities on quantum spin-1/2 Heisenberg ferromagnetic chains, revealing temperature-dependent magnetic behaviors and validating results with simulations.

Contribution

It introduces a modified spin-wave theory to analyze thermal excitations in disordered chains, capturing phenomena like Curie susceptibility and crossover behaviors.

Findings

Observation of low-temperature Curie susceptibility due to large spin clusters

Identification of a crossover to pure ferromagnetic behavior at higher temperatures

Validation of theoretical results with quantum Monte Carlo simulations

Abstract

We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute, random antiferromagnetic impurity bonds with modified spin-wave theory. By describing thermal excitations in the language of spin waves, we successfully observe a low-temperature Curie susceptibility due to formation of large spin clusters first predicted by the real-space renormalization-group approach, as well as a crossover to a pure ferromagnetic spin chain behavior at intermediate and high temperatures. We compare our results of the modified spin-wave theory to quantum Monte Carlo simulations.