講演情報
[10a-E207-5]Breakdown of phonon confinement in nanoscale membranes, beams, and phononic crystals
〇Roman Anufriev1,2, Michele Diego2, Samuel Brunot-Mueller2, Sebastian Volz1,2, Masahiro Nomura1,2 (1.LIMMS, CNRS, 2.IIS, UTokyo)
キーワード：
phonons、dispersion relation、spectroscopy
Phonon confinement is an important aspect of modern technology, as restricting vibrational modes in one or more dimensions changes the dispersion relations of phonons, which in turn affects the thermal properties of the material. Thus, understanding phonon confinement is essential for thermal management in optomechanical devices, thermoelectric generators, phononic crystals, and acoustic quantum computers. In this work, we use Brillouin-Mandelstam light scattering (BMLS), and Raman spectroscopy to experimentally probe phonon dispersion relations in nanostructures of various dimensions to find when phonons begin experiencing the dimensional confinement. We measured the dispersion relations of membranes of different thicknesses, nanowires of different widths, and phononic crystals of different periods and discovered distinct interference regimes. At the nanoscale, measured phonon dispersion relations are consistent with the elasticity theory up to at least 35 GHz. However, at larger scales and higher frequencies, phonons transition into the intermediate regime when the confinement is dominated by the smallest dimension. In even larger structures and higher frequencies, phonons cease to experience confinement altogether, and phonon transport transitions into an incoherent regime, as evidenced by the Raman spectroscopy data. These results challenge the prevailing assumption that phonon transport transitions directly from a coherent to an incoherent state at a critical frequency or size. Instead, we identify an intermediate interference regime that persists up to much higher frequencies. This refined understanding of phonon confinement improves current understanding of nanoscale thermal transport, especially at low temperatures.