Disorder Induced Phases in Higher Spin Antiferromagnetic Heisenberg Chains

TL;DR

This paper investigates how disorder affects higher spin antiferromagnetic Heisenberg chains, revealing that weak disorder is irrelevant for S=3/2 chains due to a new correlation length, contrasting with the behavior at strong disorder.

Contribution

It demonstrates that weak disorder is irrelevant for S=3/2 chains, introducing the concept of a new correlation length and expanding understanding of disorder effects in higher spin chains.

Findings

Both S=1/2 and S=3/2 chains reach a random singlet phase at strong disorder.

Weak disorder is irrelevant for S=3/2 chains, unlike S=1/2 chains.

Enhanced end-to-end correlations lead to a new correlation length.

Abstract

Extensive DMRG calculations for spin S=1/2 and S=3/2 disordered antiferromagnetic Heisenberg chains show a rather distinct behavior in the two cases. While at sufficiently strong disorder both systems are in a random singlet phase, we show that weak disorder is an irrelevant perturbation for the S=3/2 chain, contrary to what expected from a naive application of the Harris criterion. The observed irrelevance is attributed to the presence of a new correlation length due to enhanced end-to-end correlations. This phenomenon is expected to occur for all half-integer S > 1/2 chains. A possible phase diagram of the chain for generic S is also discussed.