Example: Magnetic field control of the conducting and orbital phases of layered ruthenates, J. Karpus et al., Phys. Rev. Lett. 93, (2004)  Used magnetic field control of atomic spins to sensitively manipulate orbital and conducting phases of a complex material The intellectual merits of our unique project are to:  control and study the phase behavior of “highly functional” materials as functions of temperature, magnetic field, and pressure  look in previously unexplored phase regimes of materials for highly field- and pressure-tunable properties that are of technological and scientific value: e.g., field- and pressure-tunable switching, sensing, storage, and shape memory devices Manipulating and studying the phases of functional materials with field- and pressure-tuned light scattering PI: S.L. Cooper, University of Illinois at Urbana-Champaign, DMR low temperature, 11 Tesla magnetic cryostat window scattered photon incident photon ruby chip sample gasket high pressure diamond anvil Temperature (K) Field (T) 8 20 high conducting, orbital degenerate low conducting, AF orbital ordered low conducting, FM orbital ordered

Manipulating and studying the phases of functional materials with field- and pressure-tuned light scattering PI: S.L. Cooper, University of Illinois at Urbana-Champaign, DMR Complex “functional” materials are of great interest scientifically and technologically because they exhibit highly tunable properties, i.e., their properties are exquisitely responsive to changes in externally controllable parameters, such as magnetic field, electric field, pressure, and temperature. Consequently, these highly functional materials show great promise as future switching, storage, sensing, and shape- memory devices. The goal of this project is to identify and study novel ‘highly functional’ phases of complex materials for potential applications in the next generation of “smart” and “functional” devices. To accomplish this goal, this project combines two unique elements (see top figure): (i) the ability to completely control the phase of functional materials as functions of temperature, magnetic field, and pressure; and (ii) the ability to explore – using a powerful spectroscopic technique involving light – all of the important elements of functional materials in these extreme phase regimes, namely the magnetic (spins), the conducting (electrons, orbitals), and structural (phonons) properties. As an illustration of the efficacy of this approach, we have been able to use an applied magnetic field to manipulate the orbital configuration, and therefore the conducting state, of layered ruthenate materials such as Ca3Ru2O7 (see lower figure) {J. Karpus et al., Phys. Rev. Lett. 93, (2004) }. In this study, we used the orientation of the ruthenium (Ru)-moments as a highly sensitive “spin-valve” for controlling the material’s conductivity: the high-conducting, orbital-degenerate state (red region) was induced by orienting the Ru-moments along the b-axis direction, while the low-conducting, orbital ordered state (blue region) was induced by orienting the Ru-moments along the a-axis direction. This work exploited the strong coupling between the ruthenium spins and the electronic d-orbitals (the spin-orbit coupling), which allowed us to control the orbital population on the Ru sites by orienting the atomic moments along different spatial directions using an applied magnetic field. This study shows that this material could have important device applications, particularly for situations in which one would like to control the conducting and structural properties of a device using not only the magnetic field magnitude but also the magnetic field direction.

Minjung Kim (UIUC) John Karpus (UIUC) Harini Barath (UIUC) The broader impact of this work is to:  train the next generation of scientists in cutting edge scientific and technological methods, involving the exploration of advanced materials of technological and scientific importance  to identify highly functional properties in complex materials for the next generation of switching, sensing, and storage devices Manipulating and studying the phases of functional materials with field- and pressure-tuned light scattering Example: Pressure control of the conducting and orbital phases of layered ruthenates, C.S. Snow et al., Phys. Rev. Lett. 89, (2002); J. Karpus et al., Phys. Rev. B (2005), submitted.  Used pressure to control orbital configuration and switch between high and low conducting states Graduate students supported by this project: Temperature (K) Pressure (kbar) 50 high conducting, orbital degenerate low conducting, AF orbital ordered

Manipulating and studying the phases of functional materials with field- and pressure-tuned light scattering PI: S.L. Cooper, University of Illinois at Urbana-Champaign, DMR The broader impact of this project is twofold. First, it provides training in state-of-the-art techniques (high pressure methods, low temperature methods, high field methods, optical techniques) and cutting-edge materials to several graduate students, Harini Barath, John Karpus, and Minjung Kim (top figure), two of whom are members of an underrepresented group in the physical sciences, and all of whom will be part of the next generation of scientists and engineers. Second, this work has broad impact because it involves the study of the properties of highly functional materials that show great promise as the next generation of “smart” devices. Because of the powerful spectroscopic method we employ, and our ability to completely manipulate the phase of complex materials, we are in a unique position not only to study “highly tunable” regimes of behavior that have already been identified, but also to explore new phase regimes that have not yet been discovered. As an illustration of the novel phase regimes and behavior we are capable of studying, in the bottom figure we show novel pressure-tuned “melting” behavior that we were the first to discover and explore in the layered ruthenates {C.S. Snow et al., Phys. Rev. Lett. 89, (2002)}. In this work, we were able to induce a change from a low-conducting orbital-ordered phase (blue regime), to a high-conducting orbital-degenerate phase (red regime), using applied pressure. From a technological standpoint, this result illustrates that one can sensitively control the conducting properties of these functional materials using applied strain. Scientifically, this work allowed us to investigate a novel type of “quantum melting” of a quantum ordered phase (orbital order), in which a change from an ordered configuration to a disordered configuration is induced NOT by thermal fluctuations (as in the transition from ice to water), but rather by tuning quantum mechanical parameters.