Crystal-field excitations and vibronic modes in triangular-lattice spin-liquid candidate TbInO$_3$

TL;DR

This study investigates the electronic, magnetic, and lattice properties of TbInO$_3$, revealing a non-Kramers doublet ground state, vibronic excitations, and strong spin-lattice coupling in a potential spin-liquid material.

Contribution

It provides a detailed crystal-field level scheme, identifies vibronic modes, and models spin-lattice interactions in TbInO$_3$, advancing understanding of its spin-liquid behavior.

Findings

Identified all 38 Raman-active phonon modes at low temperature.

Established the non-Kramers doublet ground state of Tb$^{3+}$ ions.

Observed hybrid vibronic excitations indicating strong spin-lattice coupling.

Abstract

We study the ground state properties, the electronic excitations and lattice dynamics in spin-liquid candidate TbInO$_3$. By employing polarization resolved Raman spectroscopy we define the inter- and intra-multiplet excitations, and establish the low-energy crystal-field (CF) level scheme. In particular, we demonstrate that the ground state of the Tb$^{3+}$ ions is a non-Kramers doublet, and relate the enhanced linewidth of the CF modes to the magnetic fluctuations near the spin-liquid ground state. We identify all 38 allowed Raman-active phonon modes at low temperature. Moreover, we observe hybrid vibronic excitations involving coupled CF and low-lying phonon modes, suggesting strong spin-lattice dynamics. We develop a model for vibronic states and obtain the parameters of the bare responses and coupling strength. We further demonstrate that the obtained CF level scheme is consistent with specific heat data.