Fig. 2: Coherent phonon oscillations and dispersions of the 8 nm/8 nm GaAs/AlAs SL excited with coincidental double pump.
From: Coherent phonon flatband generated in GaAs/AlAs superlattices via layer-selective optical pumping
a, b X-ray diffraction intensity oscillations at different Q points throughout the FBZ. XRD intensities are normalized to the respective average intensity before time zero. c, d Characteristic oscillation frequencies at each Q point, obtained from the Fourier Transform of the signals in a, b. Three distinct branches of coherent phonons can be identified: the CPFB, the FLA and FLA2. For comparison, red open circles in (d) show the phonon dispersions of the 8 nm/8 nm GaAs/AlAs SL at thermal equilibrium from the lattice dynamics calculations, including FLA1 and all the transverse phonon eigenmodes, which were not detected in the experimental data.
