Response of a Mechanical Oscillator in Solid 4He

Abstract

We present the first measurements of the response of a mechanical oscillator in solid 4 He. We use a lithium niobate tuning fork operating in its fundamental resonance mode at a frequency of around 30 kHz. Measurements in solid 4 He were performed close to the melting pressure. The tuning fork resonance shows substantial frequency shifts on cooling from around 1.5 K to below 10 mK. The response shows an abrupt change at the bcc-hcp transition. At low temperatures, below around 100 mK, the resonance splits into several overlapping resonances.

Frequency-dependent drag from quantum turbulence produced by quartz tuning forks in superfluidHe4

“…For the third overtone mode, the acoustic drag was so large that we were unable to reach the critical velocity. Furthermore, at high frequencies, anomalous behavior is often observed in the vicinity of the critical velocity, similar to that reported previously [39,47]. It has been speculated that the anomalous behavior might be due to nonlinear coupling to acoustic modes [47] and that remanent vortices spanning the prongs might also play a role [39].…”

“…The cell also contains several other devices which were not used for the current experiments, but are shown for completeness: a large lithium niobate tuning fork, a floppy wire resonator, and two pressure sensors. Experiments using these devices are described elsewhere [39,40]. Figure 1(b) shows a picture of the tuning fork assembly.…”

Stability of flow and the transition to turbulence around a quartz tuning fork in superfluidHe4at very low temperatures

“…In recent years tuning fork resonators have found a wide variety of applications in quantum fluids and solids research. They have been used to measure viscosity [1][2][3], turbulence [4,5], cavitation [6], Andreev scattering [7,8], acoustic modes [9][10][11], and the mechanical properties of solid helium [12].…”

Acoustic damping of quartz tuning forks in normal and superfluid He3

“…The interaction of helium fluids with small mechanical resonators has traditionally being studied using vibrating wires, and has led to observations of the quantization of vortices in superfluid 4 He [1,2], nucleation of quantum turbulence [3,4], and Landau critical velocity in superfluid 3 He [5]. Developments in the manufacturing of electronic components and easy access to nanofabrication facilities have brought a plethora of other mechanical devices to helium research, for example quartz tuning forks [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], micro and nanoelectromechanical devices (MEMS and NEMS) [24][25][26][27][28], optomechanical resonators [29][30][31], and carbon nanotubes [32]. Since the 2000s quartz tuning forks have become an established tool to investigate quantum solids [6] and liquids [7][8][9][10], where they have been used in studies of the viscosity [7], solubility of 4 He- 3 He mixtures [10], Andreev retroreflection of quasiparticle excitations in ...…”