Date of Graduation

5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Jak Tchakhalian

Committee Member

Laurent Bellaiche

Second Committee Member

William Oliver

Third Committee Member

Douglas Spearot

Fourth Committee Member

Paul Thibado

Keywords

Pure sciences, Complex oxides, Heterostructure, Reconstructions, Strongly correlated electrons, Superconductivity

Abstract

Strongly correlated oxides exhibit a rich spectrum of closely competing orders near the localized-itinerant Mott insulator transition leaving their ground states ripe with instabilities susceptible to small perturbations such as lattice distortions, variation in stoichiometry, magnetic and electric fields, etc. As the field of interfacial engineering has matured, these underlying instabilities in the electronic structure of correlated oxides continue to be leveraged to manipulate existing phases or search for emergent ones. The central theme is matching materials across the interface with disparate physical, chemical, electronic, or magnetic structure to harness interfacial reconstructions in the strongly coupled charge, spin, orbital, and lattice degrees of freedom. In this dissertation, we apply the above paradigm to cuprate-manganite and cuprate-titanate interfaces.

We examine ultrathin YBa2Cu3O7/La2/3Ca1/3MnO3 multilayers, where interfacial charge reconstruction modulates the distribution of charge carriers within the superconducting planes and thereby act as dials to tune through the cuprate doping phase diagram. The ultrathin nature of the cuprate layers allows the reconstructed states to be resolved free of a bulk admixture. The depleted carriers are observed to directly enter the CuO2 planes. With increasing manganite thickness, magnetic correlations are introduced, and coupling between interfacial Cu and Mn develops.

The reconstructions in spin and electronic degrees of freedom found in cuprate-manganite heterostructures are expected to completely mask all other competing interactions. To this end, SrTiO,3 is incorporated as a spacer material in cuprate-titanate multilayers to reveal the role of dimensionality, interlayer coupling, and broken translational symmetry. At the unit cell limit, a decrease in carrier concentration is found that directly correlates with underdoping from lost charge reservoir layers at the interface, while increased titanate layer thickness is found to augment the carrier concentration with the charge reservoir layers but has no effect on the doping within the superconducting planes. Also spectroscopic evidence for charge transfer across the interface between Cu and Ti is shown to support a recent theoretical prediction of pre-doping at the cuprate-titanate interface in response to a polar discontinuity at the interface.

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