Experimental properties of the A B phase boundary in superfluid "3He

This thesis describes three experiments performed on superfluid "3He at 150#mu#K. At ultra low temperatures, the entropy difference between the A and B phases is relatively large. This leads to observable thermodynamic effects when transforming one phase into another. The latent heat of the transition is related to the difference in entropy of the two phases by the Clausius-Clapeyron equation as is the critical field of the transition. We measure the temperature dependence of the both latent heat and the critical field up to temperatures of 220#mu#K. The latent heat of the transition produces observable effects when oscillating the AB interface at low frequencies. We can see the increase (decrease) in temperature of the superfluid caused by the decrease (increase) in the volume of A phase. At higher oscillation frequencies, the temperature oscillations become too fast for our thermometry time constants. However we are still able to measure the frictional dissipation of the boundary as it oscillates in the cell. The friction from Andreev scattering of quasiparticles at the boundary is predicted to behave linearly at low frequencies and become non-linear at higher frequencies as pair breaking by the moving boundary becomes the dominant friction mechanism. In fact the friction co-efficient is non-linear at all measured frequencies and the damping predicted by theory is orders of magnitude too small. The nucleation of one phase from another is subject to intense scrutiny and debate. The large entropy difference between the two phases allows us to detect exactly when the nucleation has taken place as the energy absorbed/released as a volume of one phase is changed into another is clearly visible. We observe a strong history dependence in the nucleation, in that the cell has a memory of the previous phase. We also observe that, contrary to accepted theory and experimental work, ionising radiation has no triggering effect on the B phase nucleations whereas the A phase nucleation can be triggered by ionising radiation. (author)Available from British Library Document Supply Centre- DSC:DXN057286 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo