Non-Technical Abstract: Strongly correlated oxides exhibit exciting and technologically useful properties: examples include high temperature superconductivity and colossal magnetoresistance. Recently, ruthenates became a new focus within this field since they exhibit diverse and fascinating physical properties, such as unconventional forms of superconductivity and magnetic ordering. One of the most remarkable characteristics of ruthenates is that their properties can be tuned with external stimuli such as magnetic field, chemical composition, or pressure, which offers a unique opportunity to study the physics of novel quantum phases. The goal of this Faculty Early Career Development (CAREER) project at Tulane University is to search for novel quantum phenomena in ruthenate materials and investigate their underlying physics. Understanding of novel physical phenomena in ruthenates is not only important for the development of the basic science of materials, but also has potential consequences for applications of correlated electronic materials. This project will be integrated with educational activities. A new course in materials science will be developed for Tulane Interdisciplinary Experiences program, which provides incoming freshmen students with an environment for interdisciplinary learning. Both graduate and undergraduate students will be involved in the research of this project. In addition, this project will also provide research opportunities to minority students.
Strongly correlated oxides exhibit exciting and technologically useful properties: examples include high temperature superconductivity and colossal magnetoresistance. Recently, ruthenates became a new focus within this field since they exhibit fascinating ordered ground states. Spin-triplet superconductivity, metamagnetic quantum criticality, itinerant ferromagnetism, and antiferromagnetic Mott insulating behavior have all been found in close proximity to one another. These diverse and tunable ground states offer a unique opportunity to study the physics of novel quantum phases. The goal of this Faculty Early Career Development (CAREER) project at Tulane University is to search for novel quantum phenomena in ruthenate materials and investigate their underlying physics. The specific research plan includes studies of novel quantum phase transitions, metamagnetism, bulk spin valve behavior, and orbital-related physics. Understanding of these phenomena in ruthenates is not only important for the development of the basic science of materials, but also has potential consequences for applications of correlated electronic materials. This project will be integrated with educational activities. A new course in materials science will be developed for Tulane Interdisciplinary Experiences program, which provides incoming freshmen students with an environment for interdisciplinary learning. Both graduate and undergraduate students will be involved in the research of this project. In addition, this project will also provide research opportunities to minority students.
Emergent quantum phenomena in strongly correlated materials not only hold the promise for advanced applications in energy and information technologies, but also challenge current knowledge in condensed matter physics. Strongly correlated materials refer to those materials in which electrons have a pronounced interaction with one another, thereby allowing the electrons to be controlled collectively. Phase transitions tuned by external stimuli in strongly correlated materials can occur within a time period of one picosecond or less. If such ultra-fast phase switching were applied to a transistor, it would significantly enhance the functionality. This NSF CAREER project focused on novel quantum phenomena of a complex, strongly correlated oxide system, i.e. strontium/calcium ruthenium oxide series. With the support from this project, the PI succeeded in growing high-quality single crystals of various ruthenate materials and performed systematic studies of their electronic and magnetic properties. A variety of fascinating properties have been observed, such as the bulk spin valve effect tuned by magnetic field or its orientation in Ca3Ru2O7, an antiferromagnetism-to-ferromagnetism transition tuned by charge carrier itinerancy in Ti-doped Ca3Ru2O7, an unusual quantum phase transition in close proximity to a nearly ferromagnetic state in (Sr1-xCax)3Ru2O7, and orbital selective magnetism in Sr4Ru3O10. Studies of these quantum phenomena have significantly advanced the understanding of physics of correlated electrons. In addition to studies on ruthenates, the PI has also expanded his research to the emerging field of Fe-based superconductors, which is another hot topic in condensed matter physics. The PI’s group made remarkable contributions to the understanding of the interplay between magnetism and superconductivity in the iron chalcogenide system. The PI has published a number of important papers in highly-ranked journals, including one in Nature Materials, six in Physical Review Letters, and seventeen in Physical Review B. Some of these papers have produced important impact. The PI has made significant efforts to integrate his research with education activities. He developed two new courses related to his research: "Introduction to exciting areas in materials science" and "Electronic properties of materials". The first course is a one credit hour special course developed for the Tulane Interdisciplinary Experiences (TIDES) program, aimed at introducing new Tulane students to a variety of thought-provoking subjects and providing an environment for interdisciplinary learning. The second course, "Electronic properties of materials," is offered to graduate and advanced undergraduate students. The objective of this course is to provide an introduction to the electronic and magnetic properties of materials with emphasis on the microscopic understanding of electronic and magnetic properties that are most relevant to modern device applications. Most fundamental concepts involved in the PI’s research projects are introduced in this course. In order to deepen students’ understanding of these concepts, a series of labs are offered, some of which are based on the PI’s research. Many students mentioned in their evaluation that teaching integrated with research, like in this course, is truly effective for learning. Research training is also an important part of this project. Three undergraduate students, four graduate students, and four postdocs have been involved as participants in this research project. Two graduate students received PhD degrees in 2010. One undergraduate completed the honor thesis under the PI’s guidance. The PI has also been involved in outreach activities. For example, he directed two high-school students from a local high school to do an independent research project.
