Excitations of amorphous solid helium

Abstract

We present neutron scattering measurements of the dynamic structure factor, $S(Q,\omega )$, of amorphous solid helium confined in 47 $\mathring{A}$ pore diameter MCM-41 at pressure 48.6 bar. 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 liquid-like 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 $\omega \simeq$ 0 characteristic of normal liquid ${}^4$He under pressure. Expressions for the $S(Q,\omega )$ of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid ${}^4$He 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.

References in corpus (17)

• Low Temperature Shear Modulus Changes in Solid 4-He and Connection to Supersolidity
• Disorder and the Supersolid State of Solid ${}^4$He
• Oscillation Frequency Dependence of Non-Classical Rotation Inertia of Solid ${}^4$He
• Ring exchanges and the supersolid phase of 4He
• What makes a crystal supersolid ?
• Evidence for a Superglass State in Solid 4He
• Observation of non-classical rotational inertia in bulk solid 4He
• Supersolid Helium at High Pressure
• On the origin of the decrease in the torsional oscillator period of solid He4
• Probing the Upper Limit of Nonclassical Rotational Inertia
• Thermodynamic Evidence for Nanoscale Bose-Einstein Condensation in ^4He Confined in Nanoporous Media
• Interplay of Rotational, Relaxational, and Shear Dynamics in Solid 4He
• Torsional oscillator and synchrotron x-ray experiments on solid 4He in aerogel
• ${}^4$He Crystal Quality and Rotational Response in a Transparent Torsional Oscillator
• The Anomalous Behavior of Solid ${}^4$He in Porous Vycor Glass
• Effects of ${}^3$He Impurity on Solid ${}^4$He Studied by Compound Torsional Oscillator
• Superfluidity of ${}^4$He Confined in Nano-Porous Media

Cited by in corpus (2)

• Two liquid states of distinguishable helium-4: the existence of another non-superfluid frozen by heating
• Saga of Superfluid Solids