Ultrafast formation of quantized interlayer vibrations in Bi2Se3 by photoinduced strain waves.

This study comprehensively investigated the coherent lattice dynamics in Bi2Se3 by ultrafast optical pump-probe spectroscopy with tunable near-infrared probe pulses. Sample-thickness- and probe-wavelength-dependent experiments revealed the key role of Bi2Se3 optical property in the generation and detection of photoinduced strain waves, whose confinement initiated coherent interlayer vibrations. Furthermore, the frequency and lifetime of the interlayer vibrations could be quantitatively explained with a modified linear chain and an acoustic mismatch model considering elastic coupling at sample-substrate interfaces. The results of this work provide insights for analyzing and interpreting, through ultrafast optical spectroscopy, nanomechanical interactions in layered materials.