NMR, optical, and plastic flow experiments in bcc3He ?4 He mixture crystals ? in pursuit of a vacancy fluid

The new aspects of crystal growth in solid 4 He at low temperatures are revealed by manipulating the crystal with a radiation pressure of acoustic waves. The acoustic radiation pressure is generally a tiny nonlinear effect, but it has given unexpected effect on the surface of 4 He owing to the markedly high growth rate of the crystal. Radiation pressure induces crystallization or melting. Owing to the strong temperature dependences of the growth rate of an atomically rough surface, which increases divergingly towards T ¼ 0, and the numerical value of the ratio of the sound velocities in both phases, the crystal melts at high temperatures when the sound wave is applied from the solid side, while it grows at low temperatures under the same conditions. We found a new type of growth mechanism of a c-facet driven by a strong radiation pressure. The growth rate of a c-facet was found to be much higher than the conventional screw-dislocation-mediated mechanism. Theoretical analysis that treated elementary steps as quantum mechanical quasi-particles reproduced the observed important feasures. The superflow around steps was taken into account as the kinetic energy of the steps. Finally, it was demonstrated that the use of radiation pressure enables the creation of negative crystals or superfluid bubbles in the crystal. Various interesting motions and shapes of the negative crystal were observed and interpreted using a simple model.

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“…40,41) The important point here is that dynamical motions of nagative crystals were observed and interesting new phenomena were investigated.…”

Section: Superfluid Bubble In Solidmentioning

confidence: 99%

New Aspects of Crystal Growth of Solid ⁴He Studied by Acoustic Wave

Okuda

Nomura

2008

J. Phys. Soc. Jpn.

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“…We also considered the possibility of the formation of bcc inclusions (in the P − T phase diagram the bcc phase is quite close to the solid helium region under investigation). However, T 2 in the bcc phase is about ¬0.1 − 1 s [40], which is one or two orders of magnitude higher than the times of new state.…”

Section: Discussionmentioning

confidence: 85%

NMR Study of Disordered Inclusions in the Quenched Solid Helium

et al. 2012

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Phase structure of rapidly quenched solid helium samples is studied by the NMR technique. The pulse NMR method is used for measurements of spin-lattice $T_1$ and spin-spin $T_2$ relaxation times and spin diffusion coefficient $D$ for all coexisting phases. It was found that quenched samples are two-phase systems consisting of the hcp matrix and some inclusions which are characterized by $D$ and $T_2$ values close to those in liquid phase. Such liquid-like inclusions undergo a spontaneous transition to a new state with anomalously short $T_2$ times. It is found that inclusions observed in both the states disappear on careful annealing near the melting curve. It is assumed that the liquid-like inclusions transform into a new state - a glass or a crystal with a large number of dislocations. These disordered inclusions may be responsible for the anomalous phenomena observed in supersolid region.Comment: 10 pages, 3 figure

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