Quantum Spin-Orbital Systems: Models and Spectroscopies

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TECHNICAL SUMMARY This award supports theoretical and computational research and educational activities aimed at advancing our understanding of quantum systems, in which spin and orbital degrees of freedom are strongly coupled. Relevant materials are transition metal oxides on frustrated lattices. The research has two parts. The first part is devoted to the study of the fundamental properties of strongly interacting electron systems with coupled spin and orbital fluctuations. Vanadates are perhaps the most prominent examples of spin-orbital systems. The research in this part is motivated by recent experiments on several vanadates including spinel ZnV2O4 and quasi one-dimensional CaV2O4, in which reduced dimensionality appears because of a particular structure of orbital interactions. The PI will study relevant one-dimensional spin-orbital systems. The vanadium chains in these compounds are characterized by frustrated magnetic interactions, Ising-like orbital exchanges, and a large relativistic spin-orbit interaction. Corresponding one-dimensional spin-orbital systems are in many aspects different from the famous one-dimensional SU(4) model. The PI intends to investigate these models using both analytical and numerical theoretical techniques, including bosonization and density matrix renormalization group. The second part of the proposal is devoted to the development of the theory of two-magnon and two-orbiton Raman scattering in coupled spin-orbital systems. This is a challenging but rewarding project as the theory can be readily applied to understanding a variety of existing experimental data in correlated materials with coupled spin and orbital degrees of freedom. Special emphasis will be given to the study of Raman scattering from antiferromagnets, orbitally ordered states, and spin-orbital liquids on frustrated lattices. The PI will be engaged in educational activities at the graduate level aimed at refining and enhancing courses in solid state, statistical and many-body physics. She will develop an advanced course in strongly correlated phenomena in complex systems with special emphasis on new trends in magnetism and transport phenomena. A graduate student will be involved in the research activity. The PI will organize, in collaboration with other faculty from UW-Madison, a Wisconsin Winter School on Modern Condensed Matter and Quantum Information, which will introduce young researchers to various problems in the field and will also improve collaboration between faculty, students, and postdocs from all campuses of the University of Wisconsin system. NONTECHNICAL SUMMARY This award supports theoretical and computational research and educational activities aimed at advancing our understanding of materials, in which the electron spin, an intrinsic quantum mechanical property of electrons, and the motion of the electron strongly interact with each other. The relevant materials are oxides that include transition metals, for example vanadium or zinc, with certain spatial arrangements of atoms leading to spin or spatial distribution of electrons which can occur in many nearly equivalent and hence, competing ways. Achieving a theoretical understanding of the properties of these strongly correlated materials is challenging. Interest in these systems stems in part from the richness of their novel properties: the unexpected variety of ordered states, like various forms of magnetism, the transformations among them, and their sensitivity to stresses, such as applied electric or magnetic fields. The PI will use state-of-the-art analytical as well as computational tools to investigate the physical properties of such transition metal oxides, predict new effects in these materials, and contribute to understanding of experiments. The PI will be engaged in educational activities at the graduate level aimed at refining and enhancing courses in solid state, statistical and many-body physics. She will develop an advanced course in strongly correlated phenomena in complex systems with special emphasis on new trends in magnetism and electron transport phenomena. A graduate student will be involved in the research activity. The PI will organize, in collaboration with other faculty from UW-Madison, a Wisconsin Winter School on Modern Condensed Matter and Quantum Information, which will introduce young researchers to various problems in the field and will also improve collaboration between faculty, students, and postdocs from all campuses of the University of Wisconsin system.