Quantum beat between two excitonic levels split by spin--orbit interactions in the oxychalcogenide LaCuOS.
Degenerate four-wave mixing signals excited by femtosecond laser pulses were measured in LaCuOCh (Ch = S and Se) at 4 K. The signals for LaCuOS exhibit a beat structure with a period of 480 fs just at the exciton peak energy, indicating that the lowest exciton states are split by 9 meV, but no beat structure was observed in LaCuOSe, regardless of the laser's energy. The spin--orbit interaction of the Ch ion accompanied by the hybridization of Cu 3d orbitals causes splitting of the exciton levels. Furthermore, the contribution of Ch p orbitals in the valence band maximum is larger in LaCuOSe owing to increased covalency in the Cu--Ch bond when S is replaced with Se.
Hosono Transparent Electro-Active Materials Project, ERATO, Japan Science and Technology Agency, KSP, Sakado, Takatsu-ku, Kawasaki, Japan. h-kamioka@net.ksp.or.jp
Hayato
H
Kamioka
Hidenori
H
Hiramatsu
Masahiro
M
Hirano
Kazushige
K
Ueda
Toshio
T
Kamiya
Hideo
H
Hosono