CAREER: Study of Emergent Ground States and Bosonic Excitations in Materials with Strong Spin-Lattice Coupling

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*Non-technical Abstract*Our current understanding of materials is that they are a rigid lattice of atomic nuclei, which can vibrate, but largely serve as an impartial backdrop for the motion and spinning of charged electrons. In materials where the vibrations of nuclei strongly interact with the electron spins, a number of novel behaviors have been recently reported, which are poorly understood but potentially useful for future electronic devices and energy technologies. The current project seeks to understand these behaviors through the identification of key model systems in which the effects of strong spin-lattice coupling are prominent and can be studied without additional complicating factors. Powders and large single crystals of novel materials are being prepared using equipment and expertise at the University of Illinois, and atomic motion and magnetic properties are subsequently being studied using cutting edge facilities at national laboratories. The research team is focusing specifically on behaviors deemed most promising from preliminary explorations. This work is pertinent to the understanding and control of common material properties and will help further the development of a number of new technologies. A major theme of this project is also to drive new states of matter, which might have untold useful or interesting properties. These activities provide an ideal environment for the training of graduate and undergraduate students in the methods of materials production and characterization, which is in line with current national priorities. The principal investigator is also developing a graduate course on experimental methods for studying materials at the University of Illinois, to provide greater understanding for the next generation of scientists of research opportunities open to them and to foster collaboration among student researchers. Through a series of public lectures and online exchanges, the principal investigator is also helping to educate the general populace about the science of materials, magnetism and modern experimental probes of matter.*Technical Abstract*This project seeks to identify, characterize and control the magnetic properties of materials containing a strong coupling between lattice and spin degrees-of-freedom. A joint materials development and experimental program is being pursued, where specific materials strategies will be employed to synthesize model spin-lattice coupled systems and to grow crystals, and subsequently to study them via neutron scattering and muon spin rotation using facilities at national laboratories. To maximize impact, the proposal focuses on four specific areas deemed promising from preliminary work. These include driving transitions to novel magnetic ground states with field, doping or pressure; investigating phase separation and long length-scale ordering of domains in materials; exploring how spin-lattice coupling modifies collective excitations; and creating new superconductors having strong coupling between spin and orbit angular momentum. Spin-lattice coupling effects are relevant to the discussion of a wide range of physics topics, including colossal response functions, multiferroism, superconductivity, and thermal conductivity. The current work will further discussion of these phenomena through the identification and development of model materials, where spin-lattice coupling effects can be isolated, controlled and studied directly. By studying spin-lattice coupling effects in isolation, this work will clarify the discussion and understanding of its role in more complex material systems.