Crystal-electric-field excitations in a quantum-spin-liquid candidate NaErS$_2$

TL;DR

This study investigates the crystal-electric-field excitations in NaErS$_2$, revealing nearly isotropic spins with large $J_z = frac{1}{2}$ components, supporting its potential as a quantum spin liquid host.

Contribution

The paper provides detailed CEF analysis of NaErS$_2$, demonstrating the presence of ground states conducive to quantum spin liquid behavior, which was previously limited knowledge.

Findings

Nearly isotropic spins with large $J_z=\pm 1/2$ in the ground state

CEF parameters fitted accurately using INS data

Sizable $J_z=\pm 1/2$ components suggest potential for QSL states

Abstract

The delafossite family of compounds with a triangular lattice of rare earth ions has been recently proposed as a candidate host for quantum spin liquid (QSL) states. To realize QSLs, the crystal-electric-field (CEF) ground state of the rare earth ions should be composed of a doublet that allows sizable quantum tunneling, but till now the knowledge on CEF states in the delafossite compounds is still limited. Here we employ inelastic neutron scattering (INS) to study the CEF transitions in a powder sample of the delafossite NaErS$_2$, where the large total angular momentum $J = 15/2$ of the Er$^{3+} $ ions and the resulting plethora of CEF transitions enable an accurate fit of the CEF parameters. Our study reveals nearly isotropic spins with large $J_z = \pm 1/2$ components for the Er$^{3+}$ CEF ground states, which might facilitate the development of a QSL state. The scaling of the obtained CEF Hamiltonian to different rare earth ions suggests that sizable $J_z = \pm 1/2$ components are generally present in the CEF ground states, supporting the ternary sulfide delafossites as potential QSL hosts.