Coherent Phonons in Other Materials

Recent development of ultrashort intense laser pulses has enabled the observation of small-amplitude, high-frequency phonons in wide-gap materials. Typical examples include diamond (Sect. 2.5.1), GaN [72], ZnO [73,74], and TiC 2 [75,76]. Onishi and coworkers observed the bulk and surface phonon modes of TiC 2 at four different frequencies in their TRSHG measurements 

Systematic TRSHG studies on alkali-atom adsorbed metal surfaces by Matsumoto and coworkers provided a deep insight on how coherent motions are created under very different electronic configurations [15, 77, 78]. The results showed that the coherent phonon generation critically depends on the surface and bulk electronic structure of the substrate. 

Coherent optical phonons can couple with localized excitations such as excitons and defect centers. For example, strong exciton-phonon coupling was demonstrated for lead phtalocyanine (PbPc) [79] and Cul [80] as an intense enhancement of the coherent phonon amplitude at the excitonic resonances. In alkali halides [81-83], nuclear wave-packets localized near F centers were observed as periodic modulations of the luminescence spectra. 

In a heavy fermion compound Yb MnSbn, the dephasing rate of the coherent optical phonons decreased with lowering temperature above Curie temperature Tc, but increased below Tc- The results were attributed to the coupling between an optical phonon mode and the Kondo effect [100]. 

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