Thesis defence in the University of Oulu

Doctoral Candidate

Master of Science Sami Laine

Faculty and research unit

University of Oulu Graduate School, Faculty of Science, Nano and Molecular Systems Research Unit

Field of study

Theoretical physics

Date and time of the thesis defence

28.6.2019 12:00

Place of the thesis defence

Linnanmaa, lecture hall L10

Topic of the dissertation

Spin Waves and Supercritical Motion in Superfluid He-3

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.

Dissertation

Last updated: 19.6.2019