# Dynamics of Bound Magnon Pairs in the Quasi-One-Dimensional Frustrated Magnet LiCuVO_4

## TL;DR

This study investigates the anisotropic spin dynamics in the frustrated magnet LiCuVO4 under high magnetic fields, revealing the formation of bound magnon pairs and their field-dependent excitation gaps through nuclear spin relaxation measurements.

## Contribution

It provides experimental evidence of bound magnon pairs and their dynamics in a quasi-one-dimensional frustrated magnet, confirming theoretical predictions.

## Key findings

- Transverse excitation gap increases with magnetic field.
- Longitudinal fluctuations grow at lower temperatures but decrease with higher fields.
- Anisotropic spin dynamics consistent with bound magnon pair formation.

## Abstract

We report on the dynamics of the spin-1/2 quasi-one-dimensional frustrated magnet LiCuVO$\mathrm{_4}$ measured by nuclear spin relaxation in high magnetic fields 10--34 T, in which the ground state has spin-density-wave order. The spin fluctuations in the paramagnetic phase exhibit striking anisotropy with respect to the magnetic field. The transverse excitation spectrum probed by $^{51}$V nuclei has an excitation gap, which increases with field. On the other hand, the gapless longitudinal fluctuations sensed by $^7$Li nuclei grow with lowering temperature, but tend to be suppressed with increasing field. Such anisotropic spin dynamics and its field dependence agree with the theoretical predictions and are ascribed to the formation of bound magnon pairs, a remarkable consequence of the frustration between ferromagnetic nearest neighbor and antiferromagnetic next-nearest-neighbor interactions.