High-field magnetic resonance of spinons and magnons in a triangular lattice S=1/2 antiferromagnet Cs2CuCl4

TL;DR

This study investigates high-field electron spin resonance in a triangular-lattice S=1/2 antiferromagnet, revealing the collapse of a spinon doublet and the emergence of magnon modes, shedding light on frustration effects and magnetic excitations.

Contribution

It provides experimental evidence of spinon continuum collapse and magnon behavior in Cs2CuCl4 under high magnetic fields, highlighting the role of frustration and interchain interactions.

Findings

Doublet collapses at half the saturation field

Collapse occurs at lower field than in ideal S=1/2 chain

Observation of Larmor and exchange-related magnon modes

Abstract

The electron spin resonance doublet indicating the width of the two spinon continuum in a spin-1/2 triangular-lattice Heisenberg antiferromagnet Cs2CuCl4 was studied in high magnetic field. The doublet was found to collapse in a magnetic field of a half of the saturation field. The collapse of the doublet occurs via vanishing of the high frequency component in a qualitative agreement with the theoretical prediction for the S=1/2 chain. The field of the collapse is, however, much lower than expected for the S=1/2 chain. This is proposed to be due to the destruction of frustration of interchain exchange bonds in a magnetic field, which restores the 2D character of this spin system. In the saturated phase the mode with the Larmor frequency and a much weaker mode downshifted for 119~GHz are observed. The weak mode is of exchange origin, it demonstrates a positive frequency shift at heating corresponding to the repulsion of magnons in the saturated phase.