It is widely recognized that whoever discovers and controls the optimized synthesis of novel materials generally controls the investigation of their often unique properties and, ultimately, their successful integration into advanced technologies. The proposed research is to build upon our recent success on studies on single crystals of 4d or 5d-electron-based materials and emphasize (1) the synthesis and characterization of novel transition metal oxides in bulk-single-crystal form and (2) a rigorous search for new materials. The novelty of these materials is highlighted by our recent discoveries, such as orbitally-driven colossal magnetoresistance (CMR) attained by avoiding a ferromagnetic state, and a novel spin valve effect in bulk single crystals, a delicate quantum phenomenon that depends upon precision deposition and nanoscale patterning of artificial thin-film heterostructures whose quality and performance are difficult to control. While these discoveries open new avenues for understanding the underlying physics of spintronics, and fully realizing the potential in practical devices, new physics unique to these materials, which are largely driven by spin-orbit coupling, continues to emerge, and better understanding this physics will surely lead to new discoveries. It is this new physics and possible new discoveries we seek to pursue. The transfer of technical expertise will be achieved via direct integration of the graduate students and post-docs into ongoing research efforts with a goal of professional journal publication of results. The proposed program will also constitute a key thrust within the newly established multidisciplinary Center for Advanced Materials. This association will help nurture interdisciplinary expertise that will stimulate collaborative research, and generate synergies that will attract new students who are the future human capital in technologies driving the economy.
Condensed matter physics addresses identification of novel, fundamental properties of solids and liquids that have generated a remarkable number of cutting-edge technologies in recent decades. It is widely recognized that whoever discovers and controls the optimized synthesis of novel materials generally controls the investigation of their often unique properties and, ultimately, their successful integration into advanced technologies. Unfortunately, U.S. leadership in materials research has seriously eroded in recent years due to a growing shortage of scientists who possess skills in both the synthesis and characterization of new materials. The current situation presents an urgent national challenge that could ultimately undermine our economic competitiveness if left unaddressed. The proposed research is to build upon our recent success on new materials studies and emphasize the synthesis and characterization of novel materials in bulk-single-crystal form and a rigorous search for new materials. The novelty of these materials is highlighted by our recent discoveries, such as a novel spin valve effect in bulk single crystals, a delicate quantum phenomenon that depends upon precision deposition and nanoscale patterning of artificial thin-film heterostructures whose quality and performance are difficult to control. Spin valves or more generally spintronic (magnetoelectronic) materials not only have technological potential as magnetic field sensors and read-heads for computer hard drives, but also present fundamental challenges to the theory of magnetotransport in solids. These are among the most intensively studied phenomena in materials physics and engineering due to their enormous potential impact on a $100-billion-per-year electronics industry. It is the technological potential and the intellectual challenges these materials present that we seek to pursue. The transfer of technical expertise will be achieved via direct integration of the graduate students and post-docs into ongoing research efforts with a goal of professional journal publication of results. The proposed program will also constitute a key thrust within the newly established multidisciplinary Center for Advanced Materials funded by the NSF EPSCoR RII. This association will help nurture interdisciplinary expertise that will stimulate collaborative research, and generate synergies that will attract new students who are the future human capital in technologies driving the economy.
It is widely recognized that whoever controls the synthesis and discovery of novel materials generally controls the evolution of basic research into their properties and, ultimately, their successful application in advanced technologies. The discovery and study of novel materials have been the major thrusts of our research funded by NSF. This research program combines a methodical search for novel electronic materials in single-crystal form, and a systematic effort to elucidate the underlying physics of these materials. Unique aspects of my research include: (1) advanced techniques and comprehensive facilities to synthesize bulk single crystals of new, complex oxides and chalcogenides; and (2) a wide spectrum of skills and tools for experimental studies of structural, transport, magnetic, thermal and dielectric properties as a function of temperature, magnetic field, pressure and chemical composition. Note that these studies are often carried out at low temperatures (down to 50 mK), high magnetic fields (up to 15 T) and high pressures (up to 40 kbar). It is important to realize that all the materials synthesis and characterization activities are conducted under the same roof. Transition metal oxides have recently been the subject of enormous activity within both the applied and basic science communities. However, for many decades, the overwhelming balance of interest was focused on the 3d-elements and their binary compounds. The strong magnetic and elastic properties of these materials were of primary concern, although the relatively robust superconducting properties of several Nb intermetallic compounds (e.g., Nb3Sn, NbTi) shifted some attention toward the 4d-elements during the 1960’s. A sea change occurred with the discovery of "high temperature" superconductivity in ternary and more complex copper oxides in 1986. The ongoing explosion of interest in 3d oxides produced further breakthroughs with the discovery of "colossal magnetoresistance" in ternary Mn oxides in 1990’s. It is now widely recognized that novel materials, which often exhibit surprising or even revolutionary physical properties, are necessary for critical advances in technologies that affect the lives of average people on an everyday basis. Contemporary investigators, confronted with ever-strengthening competition and ever-increasing pace in research, are beginning to examine the "unknown territories" located in the lower rows of the periodic table of the elements. Although the rare earth and light actinide elements have been well studied for many decades, the heavier 4d- and 5d-transition-metal oxides and chalcogenides have largely been ignored until recently. The reduced abundance and increased production costs for many of these elements have certainly discouraged basic and applied research into their properties. What has not been widely appreciated, however, is that 4d- and 5d-transition-metal compounds exhibit empirical trends and fundamental mechanisms that evidently produce physical behaviors that are markedly different from their 3d counterparts. In the entire life of this award, we have primarily focused on studies of single crystals of heavy transition metal oxides, particularly, iridates, ruthenates, and rhodates. These studies have led to discoveries of a wide array of novel physical phenomena seldom or never found in other materials. The primary driver of these phenomena is a strong spin-orbit interaction whose strength scales as Z4 (where Z is the atomic number). Our work has revealed that the spin-orbit interaction strongly competes with the Coulomb interaction, and certain other interactions that vigorously compete to stabilize ground states with exotic behavior. In particular, my collaborators and I have identified a most profound effect of the spin-orbit interaction in the 5d-based iridates, the Jeff = 1/2 insulating state, which is a new quantum state that exemplifies the novel physics exhibited by 5d systems. It is not surprising that heavy transition metal oxides with properties driven by the SOI are becoming the most important and challenging group of materials in contemporary condensed matter physics research. The PI is one of a few key pioneers who have initiated recent studies on iridates and, before that, ruthenates. It is important to note that our ongoing efforts to grow a large number of high-quality single crystals of iridates, ruthenates, and rhodates has made our comprehensive studies of these materials possible. These studies have not only resulted in new discoveries, but have also presented us with profound challenges that, in turn, provide strong motivation for us to broaden our studies of the novel effects of the SOI in entirely new materials---particularly those containing 5d electrons. Groundbreaking physics can certainly lead to new device applications. However, before this can be pursued, a better understanding of the physics of these novel materials needs to be established. Our major thrust has been and will continue to be physics driven by the SOI in single crystals of heavy transition metal oxides, particularly 5d-based oxides.
