Cs2CoBr4 is a triangular-lattice antiferromagnet which can be viewed as weakly interacting spin chains due to spatially anisotropic frustrating exchange couplings. The spin-orbit interaction in Co(2+) spin-3/2 ions leads to a strong easy-plane single-ion anisotropy which allows to consider the low-energy spin dynamics of this system using an anisotropic pseudospin-1/2 model. By means of the electron spin resonance (ESR) technique, we study the spin dynamics of Cs2CoBr4 in magnetic field in a spin-liquid regime, i.e., above the N'eel temperature of 1.3 K but below the temperature of the crossover to in-chain correlations of pseudospins (6 K). Our experiments reveal two bright branches of excitations which strongly differ both from excitations in the low-temperature ordered phases and from high-temperature paramagnetic resonance of uncorrelated pseudospins and spins. These two branches are interpreted as excitations with zero momentum of an anisotropic spin-1/2 chain. Besides, we observe several weak modes of unknown origin which arise mostly as satellites of one of the bright modes.
@article{arxiv.2309.02266,
title = {Dynamics of anisotropic frustrated antiferromagnet Cs2CoBr4 in a spin-liquid regime},
author = {T. A. Soldatov and A. I. Smirnov and A. V. Syromyatnikov},
journal= {arXiv preprint arXiv:2309.02266},
year = {2023}
}