On the motion of objects immersed in Fermi liquids
1University of Oulu Graduate School
2University of Oulu, Faculty of Science, Physics
|Online Access:||PDF Full Text (PDF, 1.9 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789526223056
Oulu : University of Oulu,
|Publish Date:|| 2019-08-19
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Auditorium TA105, on August 13th, 2019, at 12 o’clock noon.
Professor Erkki Thuneberg
Docent Jani Tuorila
Professor Vladimir Mineev
Professor Nils Schopohl
Professor Mikael Fogelström
Professor Erkki Thuneberg
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, ~10²³. 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.
In this thesis we study two phenomena related to the motion of objects in a Fermi liquid. First, we study the transmission of transverse oscillations through a thin film of normal Fermi liquid. The dynamics of normal Fermi liquid are described by Landau's Fermi liquid theory. Landau's theory predicts the existence of new modes of sound under conditions where sound ordinarily would not propagate. Using the equations of motion for the Fermi liquid quasiparticles, we calculate the linear response of a Fermi liquid film to the transverse oscillations of a planar substrate under a wide range of conditions. We present the linear response in terms of the film's acoustic impedance and study the effects of quasiparticle collisions and of the Fermi liquid interactions.
The second phenomenon we study is the supercritical motion of a wire in a superfluid Fermi liquid. 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. This viscosity is caused by the escape of quasiparticles, produced by pair breaking on the surface of the object, into the surrounding superfluid. We study Andreev reflection of the quasiparticles by the surrounding superfluid flow field, and modifications to the flow caused by pair breaking, as possible mechanisms for low-dissipation motion above the critical velocity.
The original publications are not included in the electronic version of the dissertation.
Report series in physical sciences
|Type of Publication:||
G5 Doctoral dissertation (articles)
|Field of Science:||
114 Physical sciences
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