Mesoscale interplay between phonons and crystal electric field excitations in quantum spin liquid candidate CsYbSe2

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 coupling resulting in a vibronic bound state. Complex, mesoscale interplay between phonon modes and CEF modes is observed in real space. Additionally, an unexpected resonant Raman excitation condition is satisfied, yielding up to third-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.

Automated summary

In this study, Raman spectroscopy is used to identify phonon and crystal electric field (CEF) modes in CsYbSe2. Strong coupling between CEF and phonon modes is observed, leading to a vibronic bound state. The complex interaction between phonon modes and CEF modes is observed in real space. Additionally, an unexpected resonant Raman excitation condition is satisfied, resulting in multiple combination modes.