On the Motion of Objects Immersed in Fermi Liquids

Interacting many-body problems are central to most fields of physics. In condensed matter physics, the systems of interest consists of a number of bodies on the order of Avogadro's constant, ~10^23. The precise modeling of such systems is usually impossible. Under certain circumstances however, even these problems can become tractable. One such circumstance is that of a Fermi liquid. At sufficiently low temperatures, in describing the dynamics of a system of interacting fermions, it is possible to forgo description of the fermions themselves, and instead concentrate on the collective excitations of the entire fermion system. These collective excitations are called quasiparticles, as they behave like weakly interacting particles. Practical examples of Fermi liquids are the conduction electrons in metals, and liquid helium-3.

In this thesis we study two phenomena related to the motion of objects in a Fermi liquid. First, we study the transmission of transverse sound waves through a thin film of normal Fermi liquid. Fermi liquid theory predicts the existence of new modes of sound under conditions where sound ordinarily would not propagate. Studying the propagation of these sound waves tells us how the fermions interact.

The second phenomenon we study is motion in a Fermi superfluid. The prevailing assumption is that if the velocity of an object moving in a superfluid Fermi liquid surpasses a characteristic critical velocity, the object experiences a sudden onset of viscous forces. Recent experiments show that in the case of a steadily moving thin wire in helium-3 superfluid, this sudden onset viscosity is not observed. We study the possible mechanisms behind this phenomenon.