Quantum Spin Dynamics Due to Strong Kitaev Interactions in the Triangular-Lattice Antiferromagnet CsCeSe$_2$

TL;DR

This study investigates the spin dynamics in the triangular-lattice antiferromagnet CsCeSe$_2$, revealing how strong Kitaev interactions lead to complex many-body phenomena and stabilize a stripe magnetic order.

Contribution

It provides the first detailed analysis of how strong Kitaev interactions influence spin excitations and phase stabilization in a triangular-lattice antiferromagnet.

Findings

Identification of magnon decay due to two-magnon continuum interactions.

Observation of spectral weight transfer to the continuum under magnetic fields.

Microscopic explanation for the stabilization of the stripe phase.

Abstract

The extraordinary properties of the Kitaev model have motivated an intense search for new physics in materials that combine geometrical and bond frustration. In this work, we employ inelastic neutron scattering, spin wave theory, and exact diagonalization to study the spin dynamics in the perfect triangular-lattice antiferromagnet (TLAF) CsCeSe$_2$. This material orders into a stripe phase, which is demonstrated to arise as a consequence of the off-diagonal bond-dependent terms in the spin Hamiltonian. By studying the spin dynamics at intermediate fields, we identify an interaction between the single-magnon state and the two-magnon continuum that causes decay of coherent magnon excitations, level repulsion, and transfer of spectral weight to the continuum that are controlled by the strength of the magnetic field. Our results provide a microscopic mechanism for the stabilization of the stripe phase in TLAF and show how complex many-body physics can be present in the spin dynamics in a magnet with strong Kitaev coupling even in an ordered ground state.