Ballistic Quasiparticles in Superfluid 3He: A Non-Newtonian Gas – George Pickett

Date: Mon. May 18th, 2009, 12:30 pm-1:30 pm
Location: Rockefeller 221

We can cool superfluid 3He to below 100 microkelvin where the number of unpaired 3He atoms is only of the order of 1 in 10^8. Here these quasiparticle excitations move ballistically as they are so tenuous that collisions are highly improbable. This dilute gas has very strange properties, since the Bardeen-Cooper-Schrieffer dispersion curve is quite unlike that for a classical gas. This makes the dynamics very unusual since even at the lowest temperatures and smallest quasiparticle energies the momentum they carry is very large. That means that we can detect this gas by its damping effect on a mechanical resonator even though by room temperature standards it would represent a reasonably good vacuum. This strange behaviour allows us to do amazing things with the gas which we use as the basic tool in all our superfluid experiments. We will discuss how the quasiparticles interact with a moving wire (quantum tennis), how the gas interacts with flow fields and finally how we can make a quasiparticle black-body radiator (but working at the microkelvin level) with almost magical thermo-mechanical properties. We also discuss the quasiparticle gas in the anisotropic A phase which is one-dimensional. Finally, we look at some of our cooling methods.