Antiferromagnetic Heisenberg chains with bond alternation and quenched disorder

TL;DR

This paper investigates the low-energy properties of antiferromagnetic Heisenberg chains with bond alternation and quenched disorder, revealing different phases depending on disorder correlation, with implications for experimental susceptibility measurements.

Contribution

It introduces a numerical strong disorder renormalization group approach to analyze phase behavior in disordered Heisenberg chains with bond alternation.

Findings

Perfect disorder correlation leads to a Griffiths phase with a concentration-dependent dynamical exponent.

Weak or no disorder correlation results in a random singlet phase with infinite dynamical exponent.

Results have implications for understanding low-temperature susceptibility in related compounds.

Abstract

We consider S=1/2 antiferromagnetic Heisenberg chains with alternating bonds and quenched disorder, which represents a theoretical model of the compound CuCl_{2x}Br_{2(1-x)}(\gamma-{pic})_2. Using a numerical implementation of the strong disorder renormalization group method we study the low-energy properties of the system as a function of the concentration, x, and the type of correlations in the disorder. For perfect correlation of disorder the system is in the random dimer (Griffiths) phase having a concentration dependent dynamical exponent. For weak or vanishing disorder correlations the system is in the random singlet phase, in which the dynamical exponent is formally infinity. We discuss consequences of our results for the experimentally measured low-temperature susceptibility of CuCl_{2x}Br_{2(1-x)}(\gamma-{pic})_2.