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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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“…Details of the displacement measurements are explained in ref. 24. It was found to be well represented by eq.…”

Section: Crystal Growth and Melting By Radiation Pressurementioning

confidence: 81%

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

Okuda

Nomura

2008

J. Phys. Soc. Jpn.

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“…Solid and dashed lines are calculated from Eqs. (1), (2), and (4) - (6). The agreement is reasonably good in the low temperature region, but other mechanisms are likely to contribute to melting at high temperatures.…”

mentioning

confidence: 56%

“…The cell had optical windows so that observation of the interface was possible at room temperature [6]. Upper and lower transducers with effective diameters of about 5 mm were placed in the cell with a separation of 10 mm.…”

mentioning

confidence: 99%

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Interface Motion and Nucleation of Solid Helium-4 Induced by Acoustic Waves

2003

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Crystallization and melting of helium-4 was experimentally observed to be induced by acoustic radiation pressure where the liquid-solid interface is highly mobile at low temperatures. We discuss the observed anomalous reversal of this effect as a function of temperature and the nucleation by acoustic wave pulses of crystals in the liquid phase or liquid bubbles in the solid phase. A high-speed camera was used for the in situ observation of large interface velocities as high as 1 m/sec.

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