Raman spectrum of hcp solid 4He.

Abstract

Raman spectra of hcp solid $^{4}\mathrm{He}$ have been measured at a temperature of 0.71 K with an instrumental resolution of 1.1 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The spectra have been confirmed to be consistent with those reported by former works: a sharp one-phonon peak is observed at 7.39\ifmmode\pm\else\textpm\fi{}0.06 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, the two-phonon spectrum appears in the energy region about 10--45 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and a broad continuous tail extends to energy shifts higher than the two-phonon region. Four peaks have been resolved in two-phonon spectra at 17.1, 20.9, 25.2, and about 30 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The two-phonon spectral structure has good qualitative similarity to that calculated theoretically by former workers. This verifies that the two-phonon spectral structure can be used for quantitative determination of parameters of lattice dynamics in quantum solids, and necessary experimental accuracy and resolution are discussed.