Ultrafast non-thermal laser excitation of gigahertz longitudinal and shear acoustic waves in spin-crossover molecular crystals [Fe(PM-AzA)(2)(NCS)(2)]

T. Parpiiev (1) , M. Servol (2) , Maciej Lorenc (2) , Ievgeniia F Chaban (1) , R. Lefort (2) , Eric Collet (2) , H. Cailleau (2) , P. Ruello (1) , Nathalie Daro (3) , Guillaume Chastanet (3) , Thomas Pezeril (1)

1 IMMM - Institut des Molécules et Matériaux du Mans
2 IPR - Institut de Physique de Rennes
3 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

We report GHz longitudinal as well as shear acoustic phonon photoexcitation and photodetection using femtosecond laser pulses in a spin-crossover molecular crystal. From our experimental observation of time domain Brillouin scattering triggered by the photoexcitation of acoustic waves across the low-spin (LS) to high-spin (HS) thermal crossover, we reveal a link between the molecular spin state and photoexcitation of coherent GHz acoustic phonons. In particular, we experimentally evidence a non-thermal pathway for the laser excitation of GHz phonons. We also provide experimental insights into the optical and mechanical parameters evolving across the LS/HS spin crossover temperature range.

Keywords: Femtosecond lasers; Photoexcitations; Chemical processes; Acoustic waves; Phonons; Light scattering

Domains: Physics [physics]

T. Parpiiev, M. Servol, Maciej Lorenc, Ievgeniia F Chaban, R. Lefort, et al.. Ultrafast non-thermal laser excitation of gigahertz longitudinal and shear acoustic waves in spin-crossover molecular crystals [Fe(PM-AzA)(2)(NCS)(2)]. Applied Physics Letters, 2017, 111 (17), 179901 (2 p.). ⟨10.1063/1.5009657⟩. ⟨hal-01681154⟩