Fred M. Ellis - Director
Department of Physics, Wesleyan University, Middletown, CT 06459
Projects and Publications
I am especially interested in this connection between the macroscopic properties and the microscopic models when the helium is adsorbed on a surface as a thin film. In this case, the physics being probed can be two dimensional. Macroscopic hydrodynamic properties are studied through the velocity and attenuation of thickness oscillations propagating in the film called "third sound". The experimental apparatus consists of a closed box, with the film adsorbed on the inner surfaces, all mounted on a dilution refrigerator able to cool the film down to below 0.05K. The third sound resonances in the box are driven and detected electrostatically with amplitude oscillations observed as either steady state resonances or as free decays.
Several problems are currently being addressed. The attenuation of the sound modes is dominated by three mechanisms: thermal exchange with the substrate, caused by temperature oscillations travelling with the wave; wave induced dissipative motion of pinned vortices (microscopic singularities of rotational flow); and harmonic pumping, in which nonlinearities associated with high amplitude waves transfer energy out of the driven mode into higher order modes. The relative importance of these mechanisms has yet to be determined. The fundamental role of Bose-Einstien condensation in the film is the focus of an experiment attempting to demonstrate the acoustic analog of a laser. Finally, persistent currents and macroscopic quantization of flow are being studied through their mutual interaction with the modes observed in the resonator where effects such as quantum swirling have been identified.
I find that the unique mixture of classical and quantum mechanics makes the study of this system particularly interesting, and enjoy working with my students on these, and related problems.
Fred M. Ellis, faculty, firstname.lastname@example.org
Josh Eddinger GRAD-ABD, email@example.com
Yudhiakto Pramudya, GRAD, firstname.lastname@example.org
Joseph Schindler, '2012, email@example.com
The past and present members of the Quantum Fluids Laboratory gratefully acknowledge support from Wesleyan University, and the National Science Foundation DMR and REU program.
Last update: January 2012. Send comments or problems with links to firstname.lastname@example.org