Magnetic excitations of the field induced states in BaCo2(AsO4)2 probed by time-domain terahertz spectroscopy

TL;DR

This study investigates magnetic excitations in BaCo2(AsO4)2 using terahertz spectroscopy, revealing field-dependent magnon behavior and the absence of quantum spin liquid signatures, thus clarifying its magnetic state.

Contribution

The paper provides the first detailed terahertz spectroscopy analysis of BaCo2(AsO4)2, showing how magnetic excitations evolve under external fields and comparing them to known Kitaev QSL candidates.

Findings

Magnetic excitations change with increasing magnetic field.

System transitions to a field-polarized paramagnetic phase beyond Hc2.

Spectra lack signatures of quantum spin liquid behavior.

Abstract

Searching for Kitaev quantum spin liquid (QSL) is a fascinating and challenging problem. Much effort has been devoted to honeycomb lattice candidates with strong spin-orbit coupling in 5d-electron iridates and 4delectron RuCl3. Recently, theoretical studies suggested that the 3d7 Co-based honeycomb materials with high spin state S=3/2 and effective orbital angular momentum L=1 could also be promising candidates of Kitaev QSL. One of the candidates, BaCo2(AsO4)2, was revisited recently. The long range magnetic order in BaCo2(AsO4)2 can be suppressed by very weak in-plane magnetic field, suggesting its proximity to Kitaev QSL. Here we perform time domain terahertz spectroscopy measurement to study the magnetic excitations on BaCo2(AsO4)2. We observe different magnon excitations upon increasing external magnetic field. In particular, the system is easily driven to a field-polarized paramagnetic phase, after the long range magnetic order is suppressed by a weak field Hc 2. The spectra beyond Hc2 are dominated by single magnon and two magnon excitations without showing signature of QSL. We discuss the similarity and difference of the excitation spectra between BaCo2(AsO4)2 and the widely studied Kitaev QSL candidate RuCl3.