Neutron Scattering Study of Quantum Phase Transitions in Integral Spin Chains

TL;DR

This paper investigates quantum phase transitions in integer spin chains using neutron scattering, revealing how magnetic excitations evolve under external magnetic fields and identifying new high-field phases.

Contribution

It provides experimental insights into the spin dynamics and phase transitions of integer spin chains, highlighting the effects of magnetic fields on magnon excitations.

Findings

Magnon gaps decrease with magnetic field leading to soft-mode quantum phase transitions.

Identification of new high-field phases with distinct spin dynamics.

Observation of Zeeman splitting effects on gapped excitations.

Abstract

Quite a few low-dimensional magnets are quantum-disordered ``spin liquids'' with a characteristic gap in the magnetic excitation spectrum. Among these are antiferromagnetic chains of integer quantum spins. Their generic feature are long-lived massive (gapped) excitations (magnons) that are subject to Zeeman splitting in external magnetic fields. The gap in one of the magnon branches decreases with field, driving a soft-mode quantum phase transition. The system then enters a qualitatively new high-field phase. The actual properties at high fields, particularly the spin dynamics, critically depend on the system under consideration. Recent neutron scattering studies of organometallic polymer crystals NDMAP (Haldane spin chains with anisotropy) and NTENP (dimerized S=1 chains) revealed rich and unique physics.