Motion of dislocations and surface steps with quantum dissipation

点击翻译按钮获取中文摘要

Some phenomena in many body system, such as motion of crystal dislocations and crystal growth of solid helium, can be reasonably described by the picture of a line. The purpose of this project is to investigate the macroscopic quantum tunneling for such processes. The group I (Suzuki, Takeuchi and Koizumi) constructed an apparatus for the deformation tests of solids in liquid ィイD13ィエD1He. Using a superconducting magnet one can measure the changes in flow stress by the super-normal transition. Experiments were performed on bcc metals and ionic crystals in which dislocation motion occures by the Peierls mechanism. Particularly the results for tantalum were analysed according to the theory published already by us, and the effective mass of a dislocation and the friction due to electrons are successfully estimated. The group II (Mizusaki and Uaha) investigated crystal growth of solid helium and obtained following results : 1) Ultra-sound velocity measurement of nuclear-ordered U2D2 solid ィイD13ィエD1He with monodomain crystal along the melting curve : The sound velocity δv/v changes as TィイD14ィエD1 below the nuclear-ordered temperature TィイD2NィエD2, 0.07% jump at TィイD2NィエD2 and takes a maximum at 3mK and decreases as T goes up. 2) Development of the MRI technique applicable at ultra-low temperatures and its application to visualization of the shape of phase separated ィイD13ィエD1He-ィイD14ィエD1He mixture. From the shape of the boundery under the gravity, we obtained the surface traction σ and the contact angle θ near the tri-critical point TィイD2tィエD2. 3) We proposed the new mechanism for solid nucleation caused by the quantum tunneling of pinning mechanism of pre-existed seed crystal on the sample wall.