可动固体$^4$ He中位错相关界面摩擦机制的观察
Observation of a Dislocation Related Interfacial Friction Mechanism in Mobile Solid $^4$He
摘要：
我们报告的温度和应力的摩擦与两个质量的固体$^4$他接触的相对运动的依赖性的研究。在扭转振子（TO）的环形样品空间中，单晶无序化过程中自发地出现了仅通过摩擦耦合的“两个质量”的情况。在TO的振荡壁施加的扭矩下，这些“质量”相对于彼此移动，在它们的界面处产生可测量的耗散。我们研究了从商业纯$^4$ He和从100 ppm的$^3$ He- $^4$ He混合物生长的固体样品在0.5 K和1.8 K之间的这种耗散。通过将TO建模为驱动谐振子来分析数据。在这个模型中，分析的谐振频率和振幅的TO产生的摩擦系数的温度依赖性。通过将数据拟合到特定形式，我们发现在我们的温度范围内，与界面运动相关的主要摩擦机制来自单个位错的攀移。与这种内部摩擦相关的特征能量标度在3 K和6 K之间，取决于样品。该能量的单个值占给定样品的数据的事实支持运动和静态固体之间的界面是良好定向的想法。在这种情况下，固体的相对运动也许可以被描述为“滑-粘”运动的下限。
英文摘要：
We report a study of the temperature and stress dependence of the friction associated with a relative motion of two masses of solid $^4$He in contact. The situation where "two masses" coupled only by friction exists emerges spontaneously during a disordering of a single crystal contained inside a annular sample space of torsional oscillator (TO). Under the torque applied by the oscillating walls of the the TO these "masses" move relative to each other, generating measurable dissipation at their interface. We studied this dissipation between 0.5K and 1.8K in solid samples grown from commercially pure $^4$He and from a 100 ppm $^3$He-$^4$He mixture. The data were analyzed by modelling the TO as a driven harmonic oscillator. In this model, analysis of the resonant frequency and amplitude of the TO yields the temperature dependence of the friction coefficient. By fitting the data to specific forms, we found that over our temperature range, the dominant friction mechanism associated with the interfacial motion results from climb of individual dislocations. The characteristic energy scale associated with this internal friction is between 3K and 6K, depending on the sample. The fact that a single value of this energy accounts for the data of a given sample supports the idea that the interface between the moving and static solid is well oriented. The relative motion of the solid in this case can perhaps be described as the low limit of "slip-stick" motion.
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