What is the relationship between the nature of a spin liquid (SL) and the crystal-field (CF) ground state? Layers of Tb ions in the ferroelectric insulator TbInO3 have been proposed to hold a two-dimensional SL ground state. By inelastic light-scattering experiments we demonstrate that the Tb ions have a non-Kramers doublet ground state, which supports a triangular magnetic lattice. In the figure at right the low-energy CF level scheme is shown, with red lines represent singlet states and blue lines doublet states. We further relate the large linewidth of CF excitations to the magnetic fluctuations near the SL ground state. Besides, we study the Raman-active phonon modes and observe hybrid vibronic excitations involving coupling CF and phonon modes. We develop a model for vibronic states and obtain the parameters of the bare responses and coupling strength.
ArXiv Link: arXiv:2105.12656 PDF: File