The transverse acoustic impedance of He II
The transverse acoustic impedance of He II
复制标题
He II 的横向声阻抗
DOI：
10.1007/bf00683280
复制
发表时间：
1984
影响因子：
2
通讯作者：
P. W. Retz
中科院分区：
文献类型：
--
作者：
M. Lea;P. Fozooni;P. W. Retz
在频率f（=ω/2π）为20.5，34.1和47.8MHz下，从30 mK到λ点Tλ（2.176K）测量了液态He Ⅱ的复剪切声阻抗。从浸没在液体中的厚度剪切模式石英晶体谐振器的品质因数和谐振频率的温度依赖性中找到了阻抗Z。流体动力学粘性液体的关系式Z（T）=（1−i）（πfηρn）1/2被用来测量粘度η（T）的温度依赖性，并使用标准流体密度ρn（T）的表列值。在λ点附近，Z（T）/Z（Tλ）与频率有关，发现超流愈合速率的值为（0.10±0.01）ε−2/3 nm，其中ε=（Tλ−T）/Tλ。还观察到晶体表面附近的货车范德华力的影响，并使用层模型来解释测量结果。在1.8 K以下，只有回旋子对Z有显著贡献，我们确定回旋子弛豫时间为τr=8.5×10− 14 T −1/3exp（8.65/T）sec。在1.2K以下，ωτr>1，我们研究了这一区域的流体力学破坏。当T <0.6 K时，晶体的共振频率降低了Δf/f=2×10−7，但这种效应的起源尚不清楚。
The complex shear acoustic impedance of liquid He II has been measured at frequenciesf(=ω/2π)of 20.5, 34.1, and 47.8 MHz from 30 mK to the λ-point Tλ(2.176 K). The impedanceZwas found from the temperature dependence of the quality factor and the resonant frequency of a thickness shear mode quartz crystal resonator immersed in the liquid. The relationship for a hydrodynamic viscous liquidZ(T)=(1−i)(πfηρn)1/2was used to measure the temperature dependence of the viscosity η(T) using tabulated values of the normal fluid density ρn(T). Deviations from hydrodynamic behavior occurred when the viscous penetration depth was less than the superfluid healing length, the phonon mean free path, and the roton mean free path. Near the λ-point,Z(T)/Z(Tλ) was frequency dependent and a value for the superfluid healing lengtha=(0.10±0.01)ε−2/3nm was found, where ε=(Tλ−T)/Tλ. The effects of van der Waals forces near the crystal surface were also observed and a layer model was used to interpret the measurements. Below 1.8 K only rotons contribute significantly toZand we determined the roton relaxation time as τr=8.5×10−14T−1/3exp (8.65/T) sec. Below 1.2 K, ωτr>1 and we investigated the breakdown of hydrodynamics in this region. ForT<0.6 K the resonant frequency of the crystals decreased by Δf/f=2×10−7, but the origin of this effect is not yet known.