Giant Physical Response in Multi-scale Inhomogeneous Oxides

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This proposal focuses on the microscopic electronic/magnetic/structural inhomogeneity found in functional oxides, and its corresponding roles in the macroscopic physical response of these materials, such as magnetoresistance, magnetic permeability, piezoelectric constants, and linear and/or non-linear optical characteristics. Understanding and controlling the inter-relationship between the inhomogeneity and physical response are of paramount importance for the development of new advanced electronic and magnetic devices. The concepts of thermodynamic or quantum criticality, soft modes, disorder effects and electronic phase separation will be important to understand the coexistence or fluctuations of neighboring phases in phase space. The activities envisioned in this program include a few important classes of complex oxide materials. The first topic is the area of magnetoresistive materials (such as CuIr2S4-CuCr2S4 and also (Bi,Sr)MnO3-(La,Sr)MnO3), showing a competition between, as well as a coexistence of, charge-ordered-insulating and ferromagnetic-metallic phases. Other topics include the enhanced piezoelectric response near MPB of ferroelectric relaxors (PMN-PT) and chemical pressure effects in geometrically frustrated antiferromagnets such as ZnCr2O4. We will also study tunneling magnetoresistance in polycrystalline films as well as a trilayer structure of double perovskite (Ca,Sr,Ba)Fe0.5Mo0.5O3. The success of this project will critically depend on a comprehensive characterization of the functional, complex oxides (or chalcogenides) as well as the fabrication of high-quality polycrystalline materials and single crystals. Materials synthesis and classical characterization including magneto-transport, susceptibility, and thermodynamic measurements will be done in the PI's lab at Rutgers University. In addition, x-ray scattering, neutron scattering, TEM, microwave, Raman, and low-temperature STM experiments will be performed through inter-institutional collaborations. This research will be conducted with the assistance of students who will thereby be prepared for entry into scientific/technological careers in industry, government or academia. %%%Modern electronic and magnetic devices often utilize physical responses of materials when the materials are exposed under external parameters such as magnetic or electric fields, pressure, or optical irradiation. Recent investigation has suggested that the large-scale physical response such as magnetoresistance, piezoelectricity, or linear and/or non-linear optical response can be drastically enhanced in materials with microscopic electronic/magnetic/structural inhomogeneity. Thus, this enhanced response in microscopically inhomogeneous materials can provide the scientific underpinning for future technologies. In this project we focus on understanding as well as controlling the inter-relationship between the microscopic inhomogeneity and macroscopic physical response. The inhomogeneity can be associated with various charge/spin/orbital degrees of freedom, and may accompany dynamic fluctuations, in addition to static spatial fluctuations. We will primarily investigate functional, complex oxides and also other chalcogenides, showing various competing or mutually antagonistic ground states. The success of this project will critically depend on a comprehensive characterization of the materials as well as the fabrication of high-quality polycrystalline materials and single crystals. Fabrication and basic characterization of the materials will be performed in the laboratory of the Principal Investigator at Rutgers University, while other more complex characterization will be performed through functioning inter-institutional collaborations. This research will be conducted with students. They will acquire advanced training in a forefront area of condensed matter physics and materials science and thus prepare them to enter the scientific/technological workforce.