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Impulsive Thermomechanics of hypersonic surface phononic crystals

F. Banfi[1], D. Nardi[2], and M. Travagliati[3]
[1]Dipartimento Matematica e Fisica, Università Cattolica, Brescia, Italy
[2]JILA, University of Colorado at Boulder, Boulder, Colorado, United States
[3]Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Pisa, Italy

Ultrafast optical generation of pseudosurface acoustic waves is investigated in hypersonic surface phononic crystals. The thermomechanics is modeled from first-principles to follow the initial impulsive heat-driven displacement in the time domain. Spectral decomposition of the displacement over the surface phononic crystal eigenmodes outlines asymmetric resonances featuring the coupling between surface and bulk modes.

This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes, and expands the present knowledge on the scattering of surface waves in mesoscale metamaterials. The theory is positively benchmarked against time-resolved optical diffraction measurements performed on surface phononic crystals.