College Park, Maryland      June 6 - 10 , 2004

WP61: Quantum momentum distribution and kinetic energy in solid 4He

S. Diallo, H. R. Glyde (Department of Physics and Astronomy, University of Delaware, Newark, DE 19716), R. T. Azuah (Department of Materials Science and Engineering, University of Maryland; NIST Center for Neutron Research)

We present measurements of neutron scattering from solid 4He at high momentum transfer. The solid is held close to the melting line at molar volume 21.0 cm3/mol and temperature T=1.6 K. From the data, we determine the shape of the momentum distribution, n(k), of atoms in the solid and the leading Final State contribution to the scattering. We show that n(k) in this highly anharmonic, quantum solid differs significantly from a Gaussian. The n(k) is more sharply peaked with larger occupation of low momentum states than in a Maxwell-Boltzmann distribution, as found in liquid 4He and predicted qualitatively by Path Integral Monte Carlo calculations. The atomic kinetic energy is < K > = 24.25+/-0.2 K. If n(k) is assumed to be Gaussian, as is usually the practice, a < K > 10% smaller is obtained.

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