Structure of end states for a Haldane Spin Chain

TL;DR

This paper investigates the edge states of finite antiferromagnetic spin-1 chains using neutron scattering, revealing staggered magnetization, inter-chain interactions, and finite-size effects on the Haldane gap.

Contribution

It provides direct experimental evidence of staggered magnetization at chain ends and characterizes the end state structure in Haldane spin chains.

Findings

Staggered magnetization at chain ends decays exponentially with a correlation length of 8.

Zeeman resonance observed below the Haldane gap at finite fields.

Finite size causes a blue shift of the Haldane gap.

Abstract

Inelastic neutron scattering was used to probe edge states in a quantum spin liquid. The experiment was performed on finite length antiferromagnetic spin-1 chains in Y_2BaNi_{1-x}Mg_xO_5. At finite fields, there is a Zeeman resonance below the Haldane gap. The wave vector dependence of its intensity provides direct evidence for staggered magnetization at chain ends, which decays exponentially towards the bulk (xi = 8(1) at T=0.1K). Continuum contributions to the chain end spectrum indicate inter-chain-segment interactions. We also observe a finite size blue shift of the Haldane gap.