4d and 5d Transition Metal Oxides: A New Frontier of Materials with Exotic Phenomena

This individual investigator award supports a systematic effort to elucidate underlying physics of the 4d and 5d transition metal oxides. These systems are a new class of materials characterized by strong coupling between different degrees of freedom and the coexistence of different kinds of ordering. Recent discoveries show a glimpse of intriguing physical properties of 4d-electron based ruthenates (Sr,Ca)(n+1)Ru(n)O(3n+1) and 5d-electron based iridates Sr(n+1)Ir(n)O(3n+1), and provide strong motivation for a thorough investigation. These layered materials exhibit an astonishing dimensionality-dependence of physical properties and a wide array of exotic phenomena including coexistence of fermion-quasiparticle and nonmetallic characteristics, inter-plane tunneling magnetoresistance, colossal magnetoresistance (CMR), drastically different anisotropies of the CMR and magnetization, p-wave superconductivity, metamagnetism, "diamagnetism" in an insulating state, etc. These phenomena reflect new physics, and it is this new physics that needs to be thoroughly studied. The planned program includes single crystal growth (both flux and floating zone methods) and experimental studies of thermal, electronic, magnetic and structural properties of these materials as a function of temperature, chemical doping, magnetic field and pressure. Graduate students involved in the research will receive rigorous training with an emphasis on materials developments, synthesis, and characterizations. This type of training in our graduate education is particularly needed nowadays as the lack of scientists who specialize in both developing new materials and growing single crystals has already hindered advancements in condensed matter physics in the US. This individual investigator award supports a systematic effort to elucidate underlying physics of the 4d and 5d transition metal oxides, which are by and large an uncharted territory rich with novel physical phenomena that cannot be explained through our conventional understanding. Recent discoveries show a glimpse of intriguing physical properties of 4d-electron based ruthenates and 5d-electron based iridates, and provide strong motivation for a thorough investigation. These layered materials exhibit an astonishing dimensionality-dependence of physical properties and a wide array of exotic phenomena including novel superconductivity and the coexistence of different kinds of ordering, which are conventionally expected to exclude each other, etc. These phenomena largely defy conventional wisdom and reflect new physics, and it is this new physics that needs to be thoroughly studied. The planned program includes materials synthesis and experimental studies of thermal, electronic, magnetic and structural properties of this class of materials as a function of temperature, chemical substitution, magnetic field and pressure. Graduate students involved in the research will receive rigorous training with an emphasis on materials developments, synthesis, and characterizations. This type of training in our graduate education is particularly needed nowadays as the lack of scientists who specialize in both developing new materials and growing single crystals has already hindered advancements in condensed matter physics in the United States.