Exchange-renormalized crystal field excitations in the quantum Ising magnet KTmSe₂

Rare-earth delafossite compounds, ARC(2) (A = alkali or monovalent ion, R = rareearth, C = chalcogen), have been proposed for a range of novel quantum phenomena. Particularly, the Tm series, ATmC(2), featuring Tm ions on a triangular lattice, serves as a representative group of compounds to illustrate the interplay and competition between spin-orbit coupling, crystal fields, and exchange couplings in the presence of geometric frustration. Here we report the thermodynamic and inelastic neutron scattering studies on the newly discovered triangular-lattice magnet KTmSe2. Both heat capacity and neutron diffraction measurements reveal the absence of long-range magnetic order. Magnetic susceptibility shows strong Ising-like interactions with antiferromagnetic correlations. Furthermore, inelastic neutron scattering measurements reveal a branch of dispersive crystal field excitations. To analyze these observations, we employ both the transverse field Ising model and the full crystal field scheme, along with exchange interactions. Our results suggest a strong competition between spin exchange interactions and crystal field effects. This work is expected to offer a valuable framework for understanding low-temperature magnetism in KTmSe2 and similar materials.