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Papers by GARY A WILLIAMS

arXiv (Cornell University), Nov 2, 2017

Journal of Low Temperature Physics - J LOW TEMP PHYS, 2000

A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height... more A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height of a few cm from the helium surface by driving a piezo transducer plate immersed under the liquid. The average droplet size is measured with a long-distance microscope and CCD camera, and ranges from about 100 µm at a drive frequency of 1 kHz to 10 µm at 100 kHz. The dependence of the droplet size on frequency is quite consistent with the capillary-wave dispersion relation of the helium surface, with the droplets ejected from the surface being about one wavelength in diameter. The initial vertical velocity of the droplets emerging from the surface is found to increase linearly with the driving voltage being applied to the piezo.

Bulletin of the American Physical Society, Mar 22, 2013

report the results of experiments on saturated superfluid 4 He films in the vicinity of the bulk ... more report the results of experiments on saturated superfluid 4 He films in the vicinity of the bulk superfluid transition temperature T λ , measuring the film thickness with a capacitance technique and the superfluid density with third sound. For moderately slow temperature sweep rates (0.5 mK/hr) we measure the critical Casimir film-thinning effect with good resolution, and find that the Kosterlitz-Thouless superfluid onset in the film occurs just at the start of the dip in film thickness. When warming through T λ at extremely slow rates (a few µK/hr), however, we have observed a sudden large increase in the film thickness (nearly 25 A in a film initially 480Å thick) within microkelvins of T λ. We propose that this is a new type of Casimir effect arising from the viscous suppression of second sound modes in the film, leading to a large free energy difference in the superfluid state that disappears abruptly when second sound ceases to propagate in the bulk helium at T λ .

Physical Review E, Apr 7, 2011

Bulletin of the American Physical Society, Mar 6, 2014

Japanese Journal of Applied Physics, 1987

The structure of vortex lines is considered for the case of very thin 4He films, where the active... more The structure of vortex lines is considered for the case of very thin 4He films, where the active super fluid thickness is less than one atomic layer. The vortex core size and core energy can be extracted from experimental studies of the finite-size Kosterlitz-Thouless transition. For pure 4He films the core size should scale as the mean separation between atoms in the active layer. This would lead to an increase in the core size as the film is thinned, and hence a progressive broadening of the finite-size KT transition as the transition temperature is reduced below 1K. The addition of 3He to the film will also increase the core size, further broadening the transition and giving rise to an initial upward shift of the apparent Tc.

Europhysics Letters, Mar 1, 2002

A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height... more A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height of 4–6cm from the helium surface by driving a piezo transducer plate immersed under the liquid. The average droplet size ranges from about 100μm at a drive frequency of 1kHz to 10μm at 100kHz, and the frequency dependence is consistent with the capillary-wave dispersion relation of the helium surface, with the droplets ejected from the surface being about one wavelength in diameter. It appears that the helium vapor is set into motion along with the droplets, greatly reducing the viscous drag on the droplets and making possible the substantial fog heights above the surface.

Bulletin of the American …, 2005

Experiments are being undertaken to measure simultaneously the Casimir film thinning effect and t... more Experiments are being undertaken to measure simultaneously the Casimir film thinning effect and the superfluidity density of 4^44He films near TlambdaT_\lambdaTlambda. A silicon substrate with nanometer-scale roughness will be employed to minimize any effects of capillary ...

Physica C: Superconductivity, 2004

Vortex-loop renormalization techniques are used to calculate the magnitude of the critical Casimi... more Vortex-loop renormalization techniques are used to calculate the magnitude of the critical Casimir forces in superfluid and superconducting thin films. The force is found to become appreciable when the size of the thermally excited vortex loops is comparable to the film thickness, and the results for T < T c are found to match very well with perturbative renormalization-group theories that can only be carried out for T > T c. In helium films the Casimir force leads to a change in the film thickness close to T c that has been observed experimentally. A similar effect is predicted to occur near the transition temperature of high-T c superconducting films, which is also a vortex-loop phase transition. In this case the Casimir force takes the form of a voltage difference that will appear at the junction between a thin film and a bulk sample. Estimates show that this voltage can be appreciable (tens of microvolts), and it may be possible to observe the effect by measuring the voltage across two Josephson tunnel junctions to the film and to the bulk, using a SQUID voltmeter.

arXiv (Cornell University), May 12, 2022

Journal of Low Temperature Physics, 1998

The super uid phase transition of 3 He-4 He mixture lms adsorbed o n 5 0 0 A alumina powder has b... more The super uid phase transition of 3 He-4 He mixture lms adsorbed o n 5 0 0 A alumina powder has been studied for mixture lms whose super uid thickness is less than a monolayer. The transitions are found to be c ontrolled by the Kosterlitz-Thouless critical line, but a strong broadening of the transition is observed a s t h e 3 He concentration is increased. Analyzing the broadening in terms of a KT vortex-pair theory modi ed for the the nite powder size yields a vortex core p arameter which increases nearly linearly with added 3 He. Also observed in these measurements is a temperature-dependent and 3 He-dependent depletion of the super uid density at low temperatures, which is thought to arise from the high-frequency ripplon third sound excitations of the lm.

Physica B-condensed Matter, Feb 1, 1994

The superfluid density of thin 4He films adsorbed in slip-cast samples of 500 A-diameter A1203 po... more The superfluid density of thin 4He films adsorbed in slip-cast samples of 500 A-diameter A1203 powder has been measured using a torsion oscillator technique. Calibration of the data shows that the superfluid transition is controlled by the universal Kosterlitz-Thouless line, as found in previous third sound studies. There is no abrupt "jump" in the superfluid density at that point, but a smooth transition that is broadened by the finite grain size of the powder. The slip-cast sample is much more homogenous than previous packed powder samples, but near Tc there is still a rounded tail to the superfluid density of about 10-15 mK.

Bulletin of the American Physical Society, Mar 15, 2021

APS March Meeting Abstracts, Mar 1, 2003

Physics, Feb 17, 2009

Imaging and tracking of bubbles in liquid helium formed by individual electrons allows study of s... more Imaging and tracking of bubbles in liquid helium formed by individual electrons allows study of superfluid vortices, and may permit analysis of unusual ionic species in fluids.

Journal of Low Temperature Physics, Mar 1, 1983

The attenuation of superfluid two-phase sound in4He is calculated and compared with experimental ... more The attenuation of superfluid two-phase sound in4He is calculated and compared with experimental results. The dispersion relation of this mode (which consists of coupled vapor sound and second sound) is determined by boundary conditions at the free liquid surface. The primary source of attenuation is found to be the evaporation-condensation process at the free surface. A calculation using kinetic models for the nonequilibrium Onsager coefficients yields an attenuation in general agreement with experimental measurements.

Physical Review Letters, Nov 19, 1984

Comment on Observation of the Formation of the Ow Pulse domain. Assuming f~'(0, II) = constant, t... more Comment on Observation of the Formation of the Ow Pulse domain. Assuming f~'(0, II) = constant, the integral can be carried over: A clear observation by optical means of the formation of zero-area pulses has recently been made by Rothenberg, Grischkowsky, and Balant. ' This characteristic pattern may occur when a propagating mode crosses another internal mode of the medium with a long enough relaxation time. In such a situa

Physical Review Letters, Feb 1, 1990

arXiv (Cornell University), Nov 2, 2017

Journal of Low Temperature Physics - J LOW TEMP PHYS, 2000

A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height... more A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height of a few cm from the helium surface by driving a piezo transducer plate immersed under the liquid. The average droplet size is measured with a long-distance microscope and CCD camera, and ranges from about 100 µm at a drive frequency of 1 kHz to 10 µm at 100 kHz. The dependence of the droplet size on frequency is quite consistent with the capillary-wave dispersion relation of the helium surface, with the droplets ejected from the surface being about one wavelength in diameter. The initial vertical velocity of the droplets emerging from the surface is found to increase linearly with the driving voltage being applied to the piezo.

Bulletin of the American Physical Society, Mar 22, 2013

report the results of experiments on saturated superfluid 4 He films in the vicinity of the bulk ... more report the results of experiments on saturated superfluid 4 He films in the vicinity of the bulk superfluid transition temperature T λ , measuring the film thickness with a capacitance technique and the superfluid density with third sound. For moderately slow temperature sweep rates (0.5 mK/hr) we measure the critical Casimir film-thinning effect with good resolution, and find that the Kosterlitz-Thouless superfluid onset in the film occurs just at the start of the dip in film thickness. When warming through T λ at extremely slow rates (a few µK/hr), however, we have observed a sudden large increase in the film thickness (nearly 25 A in a film initially 480Å thick) within microkelvins of T λ. We propose that this is a new type of Casimir effect arising from the viscous suppression of second sound modes in the film, leading to a large free energy difference in the superfluid state that disappears abruptly when second sound ceases to propagate in the bulk helium at T λ .

Physical Review E, Apr 7, 2011

Bulletin of the American Physical Society, Mar 6, 2014

Japanese Journal of Applied Physics, 1987

The structure of vortex lines is considered for the case of very thin 4He films, where the active... more The structure of vortex lines is considered for the case of very thin 4He films, where the active super fluid thickness is less than one atomic layer. The vortex core size and core energy can be extracted from experimental studies of the finite-size Kosterlitz-Thouless transition. For pure 4He films the core size should scale as the mean separation between atoms in the active layer. This would lead to an increase in the core size as the film is thinned, and hence a progressive broadening of the finite-size KT transition as the transition temperature is reduced below 1K. The addition of 3He to the film will also increase the core size, further broadening the transition and giving rise to an initial upward shift of the apparent Tc.

Europhysics Letters, Mar 1, 2002

A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height... more A dense fog consisting of superfluid 4He droplets can be generated in helium vapor up to a height of 4–6cm from the helium surface by driving a piezo transducer plate immersed under the liquid. The average droplet size ranges from about 100μm at a drive frequency of 1kHz to 10μm at 100kHz, and the frequency dependence is consistent with the capillary-wave dispersion relation of the helium surface, with the droplets ejected from the surface being about one wavelength in diameter. It appears that the helium vapor is set into motion along with the droplets, greatly reducing the viscous drag on the droplets and making possible the substantial fog heights above the surface.

Bulletin of the American …, 2005

Experiments are being undertaken to measure simultaneously the Casimir film thinning effect and t... more Experiments are being undertaken to measure simultaneously the Casimir film thinning effect and the superfluidity density of 4^44He films near TlambdaT_\lambdaTlambda. A silicon substrate with nanometer-scale roughness will be employed to minimize any effects of capillary ...

Physica C: Superconductivity, 2004

Vortex-loop renormalization techniques are used to calculate the magnitude of the critical Casimi... more Vortex-loop renormalization techniques are used to calculate the magnitude of the critical Casimir forces in superfluid and superconducting thin films. The force is found to become appreciable when the size of the thermally excited vortex loops is comparable to the film thickness, and the results for T < T c are found to match very well with perturbative renormalization-group theories that can only be carried out for T > T c. In helium films the Casimir force leads to a change in the film thickness close to T c that has been observed experimentally. A similar effect is predicted to occur near the transition temperature of high-T c superconducting films, which is also a vortex-loop phase transition. In this case the Casimir force takes the form of a voltage difference that will appear at the junction between a thin film and a bulk sample. Estimates show that this voltage can be appreciable (tens of microvolts), and it may be possible to observe the effect by measuring the voltage across two Josephson tunnel junctions to the film and to the bulk, using a SQUID voltmeter.

arXiv (Cornell University), May 12, 2022

Journal of Low Temperature Physics, 1998

The super uid phase transition of 3 He-4 He mixture lms adsorbed o n 5 0 0 A alumina powder has b... more The super uid phase transition of 3 He-4 He mixture lms adsorbed o n 5 0 0 A alumina powder has been studied for mixture lms whose super uid thickness is less than a monolayer. The transitions are found to be c ontrolled by the Kosterlitz-Thouless critical line, but a strong broadening of the transition is observed a s t h e 3 He concentration is increased. Analyzing the broadening in terms of a KT vortex-pair theory modi ed for the the nite powder size yields a vortex core p arameter which increases nearly linearly with added 3 He. Also observed in these measurements is a temperature-dependent and 3 He-dependent depletion of the super uid density at low temperatures, which is thought to arise from the high-frequency ripplon third sound excitations of the lm.

Physica B-condensed Matter, Feb 1, 1994

The superfluid density of thin 4He films adsorbed in slip-cast samples of 500 A-diameter A1203 po... more The superfluid density of thin 4He films adsorbed in slip-cast samples of 500 A-diameter A1203 powder has been measured using a torsion oscillator technique. Calibration of the data shows that the superfluid transition is controlled by the universal Kosterlitz-Thouless line, as found in previous third sound studies. There is no abrupt "jump" in the superfluid density at that point, but a smooth transition that is broadened by the finite grain size of the powder. The slip-cast sample is much more homogenous than previous packed powder samples, but near Tc there is still a rounded tail to the superfluid density of about 10-15 mK.

Bulletin of the American Physical Society, Mar 15, 2021

APS March Meeting Abstracts, Mar 1, 2003

Physics, Feb 17, 2009

Imaging and tracking of bubbles in liquid helium formed by individual electrons allows study of s... more Imaging and tracking of bubbles in liquid helium formed by individual electrons allows study of superfluid vortices, and may permit analysis of unusual ionic species in fluids.

Journal of Low Temperature Physics, Mar 1, 1983

The attenuation of superfluid two-phase sound in4He is calculated and compared with experimental ... more The attenuation of superfluid two-phase sound in4He is calculated and compared with experimental results. The dispersion relation of this mode (which consists of coupled vapor sound and second sound) is determined by boundary conditions at the free liquid surface. The primary source of attenuation is found to be the evaporation-condensation process at the free surface. A calculation using kinetic models for the nonequilibrium Onsager coefficients yields an attenuation in general agreement with experimental measurements.

Physical Review Letters, Nov 19, 1984

Comment on Observation of the Formation of the Ow Pulse domain. Assuming f~'(0, II) = constant, t... more Comment on Observation of the Formation of the Ow Pulse domain. Assuming f~'(0, II) = constant, the integral can be carried over: A clear observation by optical means of the formation of zero-area pulses has recently been made by Rothenberg, Grischkowsky, and Balant. ' This characteristic pattern may occur when a propagating mode crosses another internal mode of the medium with a long enough relaxation time. In such a situa

Physical Review Letters, Feb 1, 1990