Surfaces and Interfaces of Layered Transition Metal Oxides

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

This research project addresses the challenges and opportunities associated with the physics of broken symmetry in layered transition-metal oxides (TMOs), specifically at surfaces and interfaces. In TMOs, the strong mutual coupling between charge and spin of the electrons and the lattice degrees of freedom results in dramatic effects such as charge-, orbital-, and spin-ordering, colossal magnetoresistance, and unconventional superconductivity. Conceptually, creating a surface or interface is a controlled way to perturb the coupled system. This unique environment will produce new phenomena, while providing a fresh approach to the study of the spin-charge-lattice coupling in these complex materials. Large single crystals of naturally layered TMOs will be grown using a newly acquired NEC optical floating zone furnace, and artificially layered structures will be fabricated using laser molecular beam epitaxy (MBE). Variable-temperature scanning tunneling microscopy (STM) will be used to render spatial images of the atomic and electronic distributions at the surface. Surface structure and lattice dynamics will be determined with elastic and inelastic electron scattering. Surface magnetism will be determined both at a macroscopic and microscopic level by a combination of magneto-optical Kerr effect and variable-temperature magnetic force microscopy, with non-linear Kerr rotation used to observe buried interfaces. Synchrotron-based x-ray scattering will be utilized to measure interfacial structure. The theoretical program will use state-of-the-art first-principles computer codes, running on parallel machines, to calculate the surface structure and the electronic and magnetic properties, including stoichiometry effects. This research will be performed with graduate and undergraduate students, with the participation of postdoctoral research associates. %%% Advances in materials physics have dramatically improved our lives over the past fifty years. From the computer chip to the development of highly transparent optical fibers, from defense applications to better skis, tennis rackets, and bicycles, the availability of new materials has enabled progress in science and technology. This project, a partnership between The University of Tennessee and Oak Ridge National Laboratory (ORNL), is aimed at the development of a world-class synthesis, characterization, and educational facility for a family of materials known as transition-metal oxides (TMOs). Interest in this general class of materials stems from the richness of their physical properties (e.g., including unusual superconducting magnetic and optical properties, high temperature superconductivity, colossal magnetoresistance), complexity of their underlying physics, and the promise of technological applications. Large single crystals as well as artificially layered structures will be synthesized and studied using an extraordinary set of experimental tools (including neutron scattering at ORNL) and state-of-the-art first-principles theoretical techniques. The emphasis will be on surface and interface phenomena because of the importance of thin films in technological applications and the prospect on new emergent phenomena. The objectives are twofold: (1) to learn to tailor the electronic, magnetic, and structural surface (or interface) phase transitions in these complex TMOs for applications as sensors and transducers, and (2) to create a new, interdisciplinary curriculum and perspective on the importance of synthesis and fabrication of new materials for the advance of materials physics. The research will be conducted with graduate and undergraduate students as well as with postdoctoral research associates. They will thereby receive training in forefront research areas and be prepared to enter the scientific- technological workforce of the 21st century. ***