Facet Growth of ⁴He Crystal Induced by Acoustic Waves

Abstract

Very fast growth of the c-facet of a 4 He crystal was induced by acoustic waves. The growth velocity was larger at lower temperatures and saturated below about 400 mK. The velocity was proportional to the acoustic wave power. This fast growth cannot be explained by the spiral growth mechanism for the known value of the step mobility. We developed a step multiplication model for high-power acoustic waves and found reasonable agreement with the observed temperature and power dependence of the growth velocity.KEYWORDS: quantum solids, superfluid, acoustic radiation pressure, crystal growth, step DOI: 10.1143/JPSJ.75.023601A fundamental problem in crystal growth physics is how fast a facet can grow. In ordinary materials, the facet grows with a spiral growth mechanism well below the roughening transition temperature. 1) Step motion is limited by the diffusion of atoms and/or by the transport of latent heat. When two steps with opposite sign collide, they disappear without any reflection or transmission.Step density cannot increase indefinitely but reaches a steady-state value which is determined by the driving force for the crystallization. Recently, Parshin and Tsymbalenko have proposed a new type of collision of steps in the case of high mobility of steps at a large driving force.2) When high speed-steps collide, the steps pass through each other making another atomic layer on the facet due to the inertia of the liquid accompanying the step motion. This kinematical multiplication of steps makes the step density higher and the growth of the facet faster. Mobility of steps for a 4 He crystal in the superfluid liquid is not limited by the diffusion and can be very high at very low temperatures.3) We observed anomalously fast growth of the c-facet of a 4 He crystal induced by acoustic waves. The fast growth could not be explained by the spiral growth mechanisms and we possibly observed the multiplication of steps.We reported that acoustic waves induce crystallization of 4 He crystals at low temperatures. 4,5) We interpreted that this interface motion was induced by the acoustic radiation pressure. For the small displacement of the interface by a short acoustic wave pulse (1 ms), the acoustic radiation pressure model can explain the growth velocity of the rough and vicinal surfaces reasonably well at low temperatures by taking into account the orientation dependence of the growth coefficients. In this paper, we report the effect of the longer pulse (50 ms) applied to the vicinal surface from the crystal side. The displacement of the interface was much larger and the clear c-facet soon appeared on the top of the upheaval because the growth velocity of the c-facet was smaller than the vicinal surface. This growth velocity of the c-facet was much larger than the value expected from the spiral growth model with known step mobility. Since the pressure oscillation of the applied acoustic wave was large enough to accelerate steps to the velocity of sound, kinematical step multiplication was likely to occur. We constructed a g...

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

“…The following is a summary of typical features observed in the experiment: 8) (1) The absolute value of the growth rate was two or three orders higher than that of the spiral growth mechanism. (2) The temperature dependence of the growth rate was unique: as temperature decreased, growth rate increased, but it saturated below about 400 mK and showed no temperature dependence down to 100 mK.…”

“…They are all new phenomena and have only been investigated using acoustic wave and highly nonlinear phenomena which cannot be investigated by other methods. Most of the results presented here have already been published, [6][7][8][9] but here we offer more pictures that are not included in previous papers.…”

Asymmetry in melting and growth relaxation of4He crystals in superfluid after manipulation by acoustic radiation pressure

“…Experiments were performed in a high pressure cell that was cooled with a dilution refrigerator [20][21][22]. The high-pressure cell had two optical windows through which the inside could be observed.…”

“…4 He quantum crystals in superfluid is the exceptional material to be manipulated by small driving forces such as heat, gravity, and flow [6-13], because they grow extremely fast at low temperatures and play a very important role in understanding the fundamental aspects of crystal growth physics [14][15][16][17]. In previous reports, we have demonstrated that acoustic radiation pressure, which is the small second-order acoustic force usually not relevant to the crystallization process [18,19], induces both growth and melting of 4 He crystals and is a very useful tool to manipulate the interface in a desired orientation, even to a large extent [17,[20][21][22].…”

Bubble nucleation in a superfluid He3–He4 mixture induced by acoustic wave

“…Figure 1 shows a schematic of the experimental setup. A 3 He- 4 He dilution refrigerator is used for the experiment [10,11]. The inside of the cell can be observed through several infrared filters and infrared absorption glass from the outside.…”