CsYbSe2, a recently identified quantum spin liquid (QSL) candidate, exhibits strong crystal electric field (CEF) excitations. Here, we identify phonon and CEF modes with Raman spectroscopy and observe strong CEF-phonon mixing resulting in a vibronic bound state. Complex, mesoscale interplay between phonon modes and CEF modes is observed in real space, and an unexpected nearly resonant condition is satisfied, yielding up to fifth-order combination modes, with a total of 17 modes identified in the spectra. This study paves the way to coherent control of possible QSL ground states with optically accessible CEF-phonon manifolds and mesoscale engineering of CEF-phonon interactions.
@article{arxiv.2111.03919,
title = {Nearly-Resonant Crystalline-Phononic Coupling in Quantum Spin Liquid Candidate CsYbSe$_2$},
author = {Yun-Yi Pai and Claire E. Marvinney and Liangbo Liang and Jie Xing and Allen Scheie and Alexander A. Puretzky and Gábor B. Halász and Xun Li and Rinkle Juneja and Athena S. Sefat and David Parker and Lucas Lindsay and Benjamin J. Lawrie},
journal= {arXiv preprint arXiv:2111.03919},
year = {2022}
}