Electronic Transport Measurements in the Electron-Doped High-Temperature Superconductor Pr2-xCexCuO4-d

Abstract

This thesis is composed of four major parts centered around the electron-doped superconductor Pr2-xCexCuO4±δ: angular magnetoresistance studies of antiferromagnetism, doping effects of oxygenation, Tc enhancement by the creation of superlattices, and comparison of high-temperature resistivity with the pnictides. The first part focuses on transport measurements of the magnetism in Pr2-xCexCuO4±δ and La2-xCexCuO4±δ. It was found that the thermal evolution of the angular dependence of magnetoresistance in Pr2-xCexCuO4±δ can be used to determine the Neel temperature in that material. This angular magnetoresistance technique was also applied to La2-xCexCuO4±δ; evidence for antiferromagnetism in this system was observed as well. This section additionally develops angular magnetoresistance as a useful probe in other cuprate projects here described. The second part investigates over-oxygenated and irradiated Pr2-xCexCuO4±δ, in under- and optimal dopings. Resistivity, Hall effect, and angular magnetoresistance measurements show oxygen both doping and disordering the system, in agreement with over-doped films. The evolution of both the Hall effect and angular magnetoresistance shows that over-oxygenation results in significant changes in the number of charge carriers, regardless of the increase in scattering incurred. Additionally, this study indicates that annealing primarily removes apical oxygen, rather than other proposed behaviors. The third part studies multi-layer films of Pr2-xCexCuO4±δ and La2-xCexCuO4±δ. These superlattices exhibit a significant Tc enhancement over component layers' Tc s. Interface effects are excluded as a source of this Tc increase based upon critical current measurments. The Tc enhancement is found to be due to charge redistribution. Based on Hall and angular magnetoresistance measurements, the result of this redistribution is slightly net-under-doped films. The fourth part uses Pr2-xCexCuO4±δ and Nd2-xCexCuO4±δ as comparisons to in- vestigate the high-temperature resistivity behavior in the SrFe2As2 system. Pr2-xCexCuO4±δ and Nd2-xCexCuO4±δ are shown to be similar to other cuprate systems in that they strongly violate the Mott-Ioffe-Regel limit, an indication of strong correlations. The SrFe2As2 system was found to saturate near the Mott-Ioffe-Regel resistivity, ruling out strong, cuprate-like correlations in the pnictide superconductors. Finally, some aborted attempts at synthesis of thin films of superconducting Pr2CuO4 and iron-based superconductors are discussed. Pr2CuO4 is suggested to be an important system for understanding oxygenation in Pr2-xCexCuO4±δ.