Spin Waves and Supercritical Motion in Superfluid He-3
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Linnanmaa, lecture hall L10
Topic of the dissertation
Spin Waves and Supercritical Motion in Superfluid He-3
Doctoral candidate
Master of Science Sami Laine
Faculty and unit
University of Oulu Graduate School, Faculty of Science, Nano and Molecular Systems Research Unit
Subject of study
Theoretical physics
Opponent
PhD Mikhail Silaev, University of Jyväskylä
Custos
Professor Erkki Thuneberg, University of Oulu
Spin Waves and Supercritical Motion in Superfluid He-3
As the temperature approaches the absolute zero, the helium isotope He-3 becomes a superfluid with properties considerably different from those of conventional liquids. These properties were studied in this thesis.
Unlike ordinary liquids, a superfluid cannot rotate uniformly with the container. Instead, the vorticity is concentrated in quantised vortex lines. In the first part of the thesis, we studied how vortices affect the magnetic properties of the superfluid. We found that, under suitable conditions, the vortices interact with the magnetisation of the liquid, generating spin waves.
In the second part of the thesis, we studied the drag force exerted on an object moving in the superfluid. According to the prevailing view, the drag force is vanishingly small at low velocities, but increases abruptly as the velocity exceeds the so-called Landau critical velocity (approx. 3 cm/s at zero temperature and zero pressure). We found that this does not hold generally: if the object is macroscopic, the critical velocity may be greater than the Landau velocity. This has also recently been observed experimentally.
Unlike ordinary liquids, a superfluid cannot rotate uniformly with the container. Instead, the vorticity is concentrated in quantised vortex lines. In the first part of the thesis, we studied how vortices affect the magnetic properties of the superfluid. We found that, under suitable conditions, the vortices interact with the magnetisation of the liquid, generating spin waves.
In the second part of the thesis, we studied the drag force exerted on an object moving in the superfluid. According to the prevailing view, the drag force is vanishingly small at low velocities, but increases abruptly as the velocity exceeds the so-called Landau critical velocity (approx. 3 cm/s at zero temperature and zero pressure). We found that this does not hold generally: if the object is macroscopic, the critical velocity may be greater than the Landau velocity. This has also recently been observed experimentally.
Last updated: 1.3.2023