Correlated electrons on engineered pyrochlore lattices

Frustrated rare-earth pyrochlore titanates have been introduced as promising candidates to realize quantum spin ice (QSI). Multiple unusual quantum phases have been predicted to emerge in the QSI state upon applying a (111)-oriented external magnetic field. Here, we report the successful layer-by-layer growth of high-quality thin films of the frustrated quantum pyrochlores, R₂Ti₂O₇ (R = Dy, Ho, Er, Yb, and Tb), along the (111) direction. We confirmed their high crystallinity and proper chemical composition, discovered a robust mode of growth, and observed a pressure-sensitive growth for Tb₂Ti₂O₇. The availability of large area (111)-oriented QSI structures with planar geometry offers a new complementary to the bulk platform. The interplay between electronic interactions and strong spin-orbit coupling in pyrochlore iridates is expected to create a plethora of fascinating correlated topological states of quantum matter. Of particular interest is the Weyl semimetal phase, which was predicted to have incomplete cancellation of Chern vectors in thin-film form when the spatial inversion symmetry was broken. We report the improved solid phase epitaxy growth on Eu₂Ir₂O₇ and the first growth on Y₂Ir₂O₇ along the (111) direction. To fabricate the Eu₂Ir₂O₇ and Y₂Ir₂O₇, we developed an entirely in-situ annealing protocol. The morphological quality of the films has been confirmed by x-ray diffraction and reciprocal space mapping, demonstrating their high crystallinity with a pure pyrochlore phase and an expected epitaxial relation to the substrate. To study the interplay between 4-in-4-out and 2-in-2-out magnetic ordering, we've built two bilayer systems: Eu₂Ir₂O₇/Dy₂Ti₂O₇ and Y₂Ir₂O₇/Dy₂Ti₂O₇. The combination of the two growth mechanisms greatly improved the surface morphology and the high-temperature electrical properties of the iridates. We observed an intrinsic anomalous Hall effect with colossal coercivity. Research about the electronic and magnetic behavior when both systems order is awaiting future study.Ph.D.Includes bibliographical reference