A single chain analysis of doped quasi one dimensional spin 1 compounds: paramagnetic versus spin 1/2 doping

TL;DR

This study uses numerical methods to analyze doped spin-1 chains, revealing the stability of the Haldane phase under weak disorder and its destabilization with spin-1/2 doping, with implications for experimental observations.

Contribution

It provides a detailed numerical analysis of doped spin-1 chains, comparing paramagnetic and spin-1/2 doping effects on the Haldane phase stability.

Findings

Haldane phase remains stable under weak paramagnetic disorder

Strong disorder leads to a random singlet phase

Spin-1/2 doping destabilizes the Haldane phase even at weak disorder

Abstract

We present a numerical study of single chain models of doped spin 1 compounds. We use low energy effective one-dimensional models for both the cases of paramagnetic and spin-1/2 doping. In the case of paramagnetic doping, the effective model is equivalent to the bond disordered spin-1/2 chain model recently analyzed by means of real space renormalization group by Hyman and Yang. By means of exact diagonalizations in the XX limit, we confirm the stability of the Haldane phase for weak disorder. Above a critical amount of disorder, the effective model flows to the so called random singlet fixed point. In the case of spin-1/2 doping, we argue that the Haldane phase should be destabilized even for weak disorder. This picture is not in contradiction with existing experimental data. We also discuss the possible occurrence of (unobserved) antiferromagnetically ordered phases.