Temperature Dependence of The Sound Velocity in bcc ^3He Crystals

概要

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Longitudinal sound velocity was measured in bcc 'He crystals doped with 'Heup to 1600 ppm. The velocity usually decreased with increasing temperature,independent of the frequency between [0 and 50 MHz. The relative change in thevelocity .3v/v. was well fitted to an expression, Av/v.=k(B./B.)-pl(B./B.), whereB./B.ccT' and B./B.occ "' were respectively the relative changes in the adia-batic bulk modulus due to phonons and vacancies, and cfi':z6 K was the vacancyformation energy. It was found that k= -1.1 - -1.7 and l= -0.4 - -1.0 de-pending on the crystal, and that the two terms in Av/v. were comparable inmagnitude at T= T-. When a crystal with 480 ppm 'He was cooled bel ow 80 mK,the velocity decreased and became amplitude-dependent because of dislocationsmultiplied due to phase separation. At higher temperatures, however, no depend-ence of the velocity on the 'He concentration was observed.
社団法人日本物理学会の論文
1982-07-15