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
The work focused on two types of mixtures, 3He °He mixtures within the second
layer, and 'He 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
'He quasiparticle excitations tunneling within a solid 'He 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
An NMR spectrometer utilising a cooled differential preamplifier operating at 4K 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