Transport studies of the itinerant metamagnet Sr₃Ru₂O₇ near its quantum critical point
Abstract
Strongly correlated metals are known to give rise to a variety of exotic states.
In particular, if a system is tuned towards a quantum critical point, new
ordered phases may arise. Sr₃Ru₂O₇ is a quasi-two dimensional metal in
which field-tuned quantum criticality has been observed. In very pure single
crystals of this material, a phase with unusual transport properties forms in
the vicinity of its quantum critical point. Upon the application of a small
in-plane field, electrical resistivity becomes anisotropic, a phenomenon which
has led to the naming of this phase as an `electron nematic'.
The subject of this thesis is a study of the electrical transport in high
purity crystals of Sr₃Ru₂O₇. We modified an adiabatic demagnetisation refrigerator
to create the conditions by which the entire temperature-field phase
diagram can be explored. In particular, this allowed us to access the crossover
between the low-temperature Fermi liquid and the quantum critical region.
We also installed a triple axis `vector magnet' with which the applied magnetic
field vector can be continuously rotated within the anisotropic phase.
We conclude that the low- and high-field Fermi liquid properties have a
complex dependence on magnetic field and temperature, but that a simple
multiple band model can account for some of these effects, and reconcile the
measured specific heat, dHvA quasiparticle masses and transport co-efficients.
At high temperatures, we observe similarities between the apparent resistive
scattering rate at critical tuning and those observed in other quantum critical
systems and in elemental metals.
Finally, the anisotropic phase measurements confirm previous reports and
demonstrate behaviour consistent with an Ising-nematic, with the anisotropy
aligned along either of the principal crystal axes. Our observations are consistent
with the presence of a large number of domains within the anisotropic
phase, and conclude that scattering from domain walls is likely to contribute
strongly to the large measured anisotropy.
Type
Thesis
Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.