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 Pr_2-xCe_xCuO_{4±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 Pr_2-xCe_xCuO_{4±δ}

and La_2-xCe_xCuO_{4±δ}. It was found that the thermal evolution of the angular dependence of magnetoresistance in Pr_2-xCe_xCuO_{4±δ} can be used to determine the Neel temperature in that material. This angular magnetoresistance technique was also applied to

La_2-xCe_xCuO_{4±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 Pr_2-xCe_xCuO_{4±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 Pr_2-xCe_xCuO_{4±δ} and La_2-xCe_xCuO_{4±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 Pr_2-xCe_xCuO_{4±δ} and Nd_2-xCe_xCuO_{4±δ} as comparisons to in-

vestigate the high-temperature resistivity behavior in the SrFe₂As₂ system. Pr_2-xCe_xCuO_{4±δ}

and Nd_2-xCe_xCuO_{4±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 Pr_2-xCe_xCuO_{4±δ}.