Correlated Metals as Visible and Ultraviolet Transparent Conductors
Open Access
- Author:
- Roth, Joseph Dennis
- Graduate Program:
- Materials Science and Engineering (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 06, 2021
- Committee Members:
- Rongming Chu, Outside Unit & Field Member
Venkatraman Gopalan, Major Field Member
Jon-Paul Maria, Major Field Member
Roman Engel-Herbert, Chair & Dissertation Advisor
John Mauro, Program Head/Chair - Keywords:
- Transparent conductor
Correlated metal
Molecular beam epitaxy
Thin film
Perovskite oxide - Abstract:
- While modern physics offers accurate descriptions of many material classes such as conductors and insulators, there are some peculiar subgroups that lie outside complete theoretical understanding. One such class is that of correlated materials where the coulombic interactions between electrons are simply too strong to be ignored. These materials have been observed to exhibit profound properties due to the interplay between the charge, spin, and orbital moment of their d- and f- electrons. The complex interactions between these electrons are extremely sensitive to defects, chemical composition, and external stimuli, making it decidedly difficult to experimentally verify theoretical models and predictions. This problem is further amplified by the inherent difficulty in synthesizing many of these complex, multicomponent materials which host intriguing properties arising from a sizeable electron correlation. Even with advances in modern thin film growth techniques such as molecular beam epitaxy and pulsed laser deposition, high quality material synthesis remains one of the leading challenges in the field of experimental correlated materials. In addition, the recent discovery of certain correlated metals as transparent conducting materials has added a technological desire to expand material solutions beyond the conventional composition and design space of transparent conductors. This thesis addresses three open questions in the field of experimental correlated materials using the perovskite correlated metals SrVO3 and SrNbO3: how can electron correlations be utilized in room temperature applications, how does disorder and anisotropic scattering influence properties arising from electron interactions, and how does film orientation affects electronic transport in correlated metals. The first question is addressed through the experimental verification of SrNbO3 as an effective UV transparent conductor which was found to have an optical transmission up to 94% at a wavelength of 280 nm with a resistivity of 2.36×10-4 Ωcm. The second question is then addressed by investigating the influence of disorder in SrVO3 films where a robust Fermi liquid phase was found to exist at low temperature. The scattering prefactor in the Fermi liquid phase was found to be dependent on anisotropic scattering arising from the Fermi surface geometry in the ultraclean limit. Finally, the dependence of electronic properties on film orientation was investigated by growing [111]-oriented SrVO3 where significant alterations to the electronic transport were observed in comparison to [001]-oriented films. This thesis is structured as follows. First, an introduction to traditional metals, correlated metals, and electron-electron interactions is presented in Chapter 1. A short review of transparent conductors in the visible and ultraviolet regions as well as recent developments in the growth of correlated metals along the polar [111] direction are also included. Chapter 2 provides a review of the experimental growth techniques and characterization methods used for these correlated materials. Chapter 3 then delves into the structural, electrical, and optical characterization techniques used in this thesis. Exploration into room temperature applications for correlated materials begins in Chapter 4 with the theoretical and experimental investigations of SrNbO3 as a visible and ultraviolet transparent conductor. Chapter 5 expands this investigation by examining the role of Sr vacancies in sputtered SrxNbO3 films. The effects of material quality and the entanglement of electron-electron scattering and disorder are then studied in Chapter 6 with SrVO3 grown by hybrid molecular beam epitaxy. Finally, Chapter 7 demonstrates the growth of SrVO3 in the polar [111]-orientation and the subsequent, unexpected effects on the electronic transport. The work presented here offers insights to both technological advances and fundamental research of correlated materials. This dissertation offers fertile ground to inspire future advancements in the fields of experimental correlated metals, transparent conducting materials, hybrid MBE, and topological materials.