At low temperatures, strongly correlated materials, which typically contain partially filled d- or f-electron shells, often exhibit phases with interesting properties,
which may be of both research value and technological significance. The mechanisms of phase formation in them if could be clarified, are believed to be able
to provide important insights not only into physics but also into the design of
new materials. In this thesis, the experimental study of two strongly correlated
materials, Sr₂RuO₄ and CeAuSb₂ is presented.
Sr₂RuO₄ is an unconventional superconductor, and a strong candidate for spin-triplet superconductivity. Its potential significance in relation to quantum computing also makes it of great scientific interest. In order to clarify the role of the
Van Hove singularity (VHS) in its superconductivity, experimental study has been
performed with the recently developed uniaxial strain methods. The experimental
results suggest that as the sample is compressed towards the VHS, the transition
temperature can be enhanced by a factor of =2.3 whilst the upper critical field
can be enhanced by a factor of more than ten. The experimental findings are
intriguing and new possibilities are open for future study.
CeAuSb₂ is a Kondo lattice system which has been speculated to be close to
a quantum critical point. The similarity between some of its low temperature
properties and those of a well-known quantum critical system Sr₃Ru₂O₇ makes
it especially interesting. In this thesis, new magnetoresistivity and torque magnetometry measurements are used to clarify its low temperature phase diagram, and
reveal the strength of its magnetic anisotropy
