Novel States in Spin-Orbit-Coupled and Correlated Materials

The proposed research encompasses a systematic effort to elucidate physics of novel phenomena in spin-orbit-coupled materials and a rigorous search for new materials having exotic states. Intellectual Merits: Physics driven by spin-orbit interactions (SOI) is among the most current and important topics in contemporary condensed matter physics. The 4d- and 5d-elements constitute two thirds of the d-transition elements listed in the Periodic Table, and materials containing these elements are a particularly fertile ground for studies of new physics since SOI is comparable to the on-site Coulomb and other relevant interactions, thus creates an unique balance between competing interactions that drives complex behaviors and exotic states often absent in other materials. We have already uncovered a large number of fundamental characteristics unique to these materials that defy conventional physics: No metallization achieved at high pressures, no conventional correlations between magnetic and insulating states, and a possible odd-parity hidden order existent in 5d-based iridates; contradictory coexistence of a bulk insulating state and quantum oscillations period in 1/B or B (depending on the orientation of B, which is applied magnetic field) and colossal magnetoresistivity without spin polarization in 4d-based ruthenates. Accordingly, this proposal will focus on the following areas: (1) Novel states at high pressures and high magnetic fields, (2) Unusual correlations between the insulating gap and magnetic transition in iridates and ruthenates, (3) Exotic metallic and superconducting states in iridates, (4) d4-Mott insulators with "intermediate-strength" SOI and other competing energies in materials having d4 ions, (e.g., Ru4+(4d4), Rh5+(4d4), Re3+(5d4), Ir5+(5d4), etc.), and (5) Single-crystal synthesis and search for novel materials. We are uniquely positioned to pursue the proposed project, as the PI is one of a few key pioneers who have initiated recent studies on iridates and, before that, ruthenates. We have comprehensive facilities and proven expertise for single-crystal synthesis and studies of structural, transport, magnetic, thermal and dielectric properties as a function of temperature, magnetic field, pressure and chemical doping. Broader Impact: Emerging technologies increasingly require high quality, bulk single crystals for definitive studies of fundamental properties, and successful integration of their novel properties into state-of-art device structures. Investigators who are able to first synthesize high-quality samples of novel materials are in an optimal position to discover their often unique properties and, ultimately, to lead efforts to apply them in advanced technologies. Unfortunately, U.S. leadership in Condensed Matter Physics has severely eroded, mainly due to a lack of scientists who possess skills in both synthesis and characterization of new materials. The current situation could ultimately undermine our economic competitiveness if left unaddressed. We provide all students involved rigorous training that emphasizes both synthesis and characterization techniques covering a broad spectrum of materials and experimental probes that are available in the PI's lab. They will also be trained via short courses, national lab visits, paper and proposal writing. The proposed program will also constitute a key thrust within the Center for Advanced Materials where the PI is Director. This association will help nurture interdisciplinary expertise that will generate synergies and attract new students who are the future human capital in technologies driving the economy. In addition, we will continue to generate high-quality single crystals in support of our extensive collaborations with over a dozen colleagues, which has already helped and will continue to help advance their research and our collective understanding of the novel phenomena under study.