Mesoscale interplay between phonons and crystal electric field excitations in quantum spin liquid candidate CsYbSe2†‡
Yun-Yi
Pai, 
*ab
Claire E.
Marvinney,
ab
Liangbo
Liang,
c
Jie
Xing,
a
Allen
Scheie,
d
Alexander A.
Puretzky,
c
Gábor B.
Halász,
ab
Xun
Li,
a
Rinkle
Juneja,
a
Athena S.
Sefat,
a
David
Parker,
a
Lucas
Lindsay
a
and
Benjamin J.
Lawrie
*ab
*ab
Claire E.
Marvinney,
ab
Liangbo
Liang,
c
Jie
Xing,
a
Allen
Scheie,
d
Alexander A.
Puretzky,
c
Gábor B.
Halász,
ab
Xun
Li,
a
Rinkle
Juneja,
a
Athena S.
Sefat,
a
David
Parker,
a
Lucas
Lindsay
a
and
Benjamin J.
Lawrie
*ab
Abstract
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.
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