Spin-Triplet Excitons in the $S=1/2$ Gapped Antiferromagnet BaCuSi$_2$O$_6$: Electron Paramagnetic Resonance Studies

TL;DR

This study uses electron paramagnetic resonance to investigate spin-triplet excitons in BaCuSi$_2$O$_6$, revealing a thermally-activated superstructure and providing detailed anisotropy parameters.

Contribution

It presents the first detailed EPR analysis of spin-triplet excitons in BaCuSi$_2$O$_6$, elucidating their structure and anisotropy.

Findings

Multiple low-temperature absorptions linked to spin-triplet excitons

Accurate estimation of anisotropy parameters from angular dependence

Temperature effects on EPR intensity and linewidth

Abstract

BaCuSi$_2$O$_6$, a $S=1/2$ quantum antiferromagnet with a double-layer structure of Cu$^{2+}$ ions in a distorted planar-rectangular coordination and with a dimerized spin singlet ground state, is studied by means of the electron paramagnetic resonance technique. It is argued that multiple absorptions observed at low temperatures are intimately related to a thermally-activated spin-triplet exciton superstructure. Analysis of the angular dependence of exciton modes in BaCuSi$_2$O$_6$ allows us to accurately estimate anisotropy parameters. In addition, the temperature dependence of EPR intensity and linewidth is discussed.