Adrian F.G. Wyatt Research Interests

Ripplons at the Helium-Cesium interface

The interface between liquid ⁴He and cesium is very interesting. A pure cesium surface presents the weakest binding substrate for liquid ⁴He and we have recently shown that the liquid ⁴He at this interface behaves very similarly to the free liquid surface. This is a very surprising result and is obtained from measuring the contact angle of ⁴He on cesium below the wetting temperature. We are currently studying ³He bound states at this interface and have designed a new experiment to measure the contact angle at the lower wetting temperature.

Mobility Hydrogen in Two Dimensional Films

The surface of solid H₂ is much more mobile than other solids. We have studied films of hydrogen which are four layers thick, and by creating holes in these films we can watch their return to equilibrium. This is done by evaporating molecules and measuring the flux with a bolometer. We have developed a model that accounts for these measurements which shows that the hydrogen molecules move by thermally activated diffusion.

Creation of High-Energy Phonons

We are currently developing a model for the creation of high energy phonons in liquid helium. A propagating cloud of low energy phonons creates high-energy phonons by phonon-phonon up-scattering and once they reach a certain critical energy they are relatively stable.The high energy phonons are lost out of the back of the cloud as their group velocity is less than that of the low energy phonons. This process is very efficient in transforming energy from low to high energy phonons which agrees with experiments.

Next: The Quantum Interacting Systems Research Group
See also: Physics Research at Exeter