Second Sound in Solid Helium

Abstract

An experiment on temperature pulse propagation in a bcc crystal of $^{3}\mathrm{He}$ grown at 95.9 atm shows the existence of second sound in the solid below about 0.58\ifmmode^\circ\else\textdegree\fi{}K. In the temperature range $0.42\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}lTl0.58\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}$, reflections of the received pulses were observed. In the range $0.58\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}lTl1.2\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}$, the temperature pulses were observed to propagate diffusively.