Probably the most significant challenge facing condensed matter physics today is to understand metallic behavior that falls outside the independent electron approximation. The number of metallic systems for which this approximation fails is small but these systems are of exceptional interest because they often display exciting phenomena like high-Tc superconductivity. Additionally, these systems exhibit a common pattern of anomalies, giving us hope that there is a universal physical picture by which we can understand them. Two of these anomalies are in the charge transport sector: a T-linear resistivity and a strongly T-dependent Hall effect. This dissertation seeks to extend this pattern by studying the charge transport properties of the iron-pnicited superconductor BaFe2(As1-xPx)2 at very high magnetic fields. The data obtained in these experiments reveal significant magnetic analogues of both the aforementioned anomalous temperature dependencies, and confirm that the dynamics in this system conform to two of the predictions of quantum critical theory: scale invariance and the existence of a uniform fan-like region around the quantum anti-ferromagnetic quantum phase transition. These findings support the hypothesis that quantum criticality is at the root of these particular anomalies, while simultaneously challenging the naive version of the theory and creating new opportunities for investigating the microscopic nature of the strongly correlated state.

# Your search: "author:"Analytis, James G""

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Transition metal oxides are fascinating and complex materials that have puzzled condensed matter physicists for many years due to their many different electronically ordered ground states. Albeit separated by external or internal parameters, these nearly degenerate phases are sometimes intertwined in competition or coexistence, which can itself lead to further phase emergence.

A unique feature of the 5d iridium oxide materials is that spin-orbit and Coulomb interactions are of comparable strength and therefore compete vigorously. In a honeycomb structure, this competition gives rise to strong magnetic frustration due to their edge-shared bonding environment, in which quantum interference of the two exchange paths favors a strongly anisotropic, Ising-like exchange between neighboring spin-1/2 moments. Such an interaction couples different orthogonal spin components for the three nearest neighbors and, as a consequence, no single exchange direction can be simultaneously satisfied, leading to strong frustration described by the Kitaev Hamiltonian. This model results in the infinitely degenerate and extremely exotic quantum spin liquid state, whose excitations range from being Majorana-like to fractionalized fermionic excitations. In this thesis, I examine the magnetic properties of the three-dimensional Kitaev candidate materials in the Harmonic Honeycomb family, using a combination of thermodynamics and resonant x-ray scattering techniques.