Zeeman levels with exotic field dependence in the high field phase of a S=1 Heisenberg antiferromagnetic chain

TL;DR

This study investigates the Zeeman level behavior in a high-field phase of an S=1 Heisenberg antiferromagnetic chain using ESR measurements, revealing exotic field dependence and matching phenomenological theory.

Contribution

It provides experimental ESR data on a quasi-1D S=1 antiferromagnet and demonstrates theoretical modeling of Zeeman levels with complex-field $$ theory.

Findings

Observation of gapped excitation branches above critical field

Agreement between experimental data and phenomenological theory

Identification of exotic field dependence in Zeeman levels

Abstract

We have performed electron spin resonance measurements over a wide frequency and magnetic field range on a single crystal of the S=1 quasi-one-dimensional Heisenberg antiferromagnet $\rm Ni(C_5H_{14}N_2)_2N_3(PF_6)$. We observed gapped excitation branches above the critical field ($H_{\rm c}$) where the Haldane gap closes. These branches are analyzed by a phenomenological field-theory using complex-field $\phi^{4}$ model. A satisfactory agreement between experiment and theory is obtained.