Experimental study of two-dimensional helium mixture films absorbed on graphite

"3He-"4He mixture films adsorbed on graphite were studied down to temperatures below 1 mK using heat capacity and nuclear magnetic resonance (NMR) to probe the system. This work represents the first measurements in this temperature range of the various systems studied. The work focused on two types of mixtures, "3He-"4He mixtures within the second layer, and "3He floating on three layers of "4He. For mixtures within the layer, a homogeneous mixed phase was observed, followed by a phase interpreted as a Fermi liquid of "3He quasiparticle excitations tunneling within a solid "4He lattice. For the second type of mixture, the expected occupancy of the first excited surface normal state was observed. This is accompanied by anomalous behaviour at low temperatures (T < 10 mK) which arises due to a low concentration of "3He atoms being pushed into the third superfluid "4He layer. An NMR spectrometer utilising a cooled differential preamplifier operating at 4 K was developed and used to measure the magnetic properties of helium mixtures. However, its signal to noise ratio was too low to provide the required accuracy in the measurements. An automated computer controlled data acquisition system was also developed to measure heat capacity and magnetic properties of the mixtures. The accompanying software required to process the data collected from both types of measurements was also developed and used successfully to obtain the data presented in this thesis. (author)Available from British Library Document Supply Centre- DSC:DXN059215 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo