Excitations Of Amorphous Solid Helium

We present neutron scattering measurements of the dynamic structure factor S(Q,omega) of amorphous solid helium confined in 47-angstrom pore diameter MCM-41 at pressure 48.6 bars. At low temperature T = 0.05 K, we observe S(Q,omega) of the confined quantum amorphous solid plus the bulk polycrystalline solid between the MCM-41 powder grains. No liquidlike phonon-roton modes, other sharply defined modes at low energy (omega < 1.0 meV), or modes unique to a quantum amorphous solid that might suggest superflow are observed. Rather, the S(Q, omega) of confined amorphous and bulk polycrystalline solid appear to be very similar. At higher temperature (T > 1 K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad S(Q,omega) peaked near omega similar or equal to 0, characteristic of normal liquid He-4 under pressure. Expressions for the S(Q,omega) of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid He-4 confined in MCM-41 at lower pressure, the intensity in the liquid roton mode decreases with increasing pressure until the roton vanishes at the solidification pressure (38 bars), consistent with no roton in the solid observed here.