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.
© 2004 Optical Society of America
(160.4670) Materials : Optical materials
(160.6000) Materials : Semiconductor materials
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
(300.6290) Spectroscopy : Spectroscopy, four-wave mixing
Hayato Kamioka, Hidenori Hiramatsu, Masahiro Hirano, Kazushige Ueda, Toshio Kamiya, and Hideo Hosono, "Quantum beat between two excitonic levels split by spin-orbit interactions in the oxychalcogenide LaCuOS," Opt. Lett. 29, 1659-1661 (2004)