Exploring Novel Quantum Materials with Neutrons and X-rays

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The goal of this research program is to investigate the structural, magnetic, and electronic properties of a novel class of materials: spin-orbit-driven quantum materials. This family of materials displays unique physical properties due to strong spin-orbit coupling, i.e. the interaction between the spin of a particle and its orbital motion. The strength of spin-orbit coupling increases with atomic mass, meaning it plays a much more significant role in materials based on heavy transition metal elements such as iridium. This strong spin-orbit coupling can have a profound effect on the physics of heavy transition metal compounds, giving rise to a host of exotic quantum ground states. It can drive the formation of a novel insulating state, the spin-orbital Mott insulator, in materials which would otherwise behave like metals. It also changes the nature of magnetic moments, entangling spin and orbital moments to form a total effective angular momentum (Jeff). A particularly interesting phenomenon can arise in spin-orbit-driven materials which: (a) behave as spin-orbital Mott insulators, (b) possess small, inherently quantum mechanical, Jeff = 1/2 magnetic moments, and (c) display a crystal structure based on edge-sharing octahedra. Under these conditions, the conventional Heisenberg magnetic interaction can cancel out, leaving an exotic bond-dependent magnetic interaction known as the Kitaev interaction. Most notably, in materials with a honeycomb lattice crystal structure, these interactions can produce a Kitaev quantum spin liquid (QSL), a rare quantum state which remains magnetically disordered down to the lowest possible temperatures. The excitations of this state display unusual anyonic statistics, suggesting that the Kitaev QSL could provide the building blocks for a fault-tolerant topological quantum computer. Although several promising candidates have been identified (e.g. A2IrO3, RuCl3, H3LiIr2O6), identifying a suitable experimental realization of the Kitaev QSL state remains an ongoing challenge. In this research program, I propose to (a) synthesize new spin-orbit-driven quantum materials and potential Kitaev QSL systems, (b) characterize the properties of these materials using synchrotron x-ray and neutron scattering techniques, and (c) tune these properties via chemical doping, intercalation, applied pressure, and magnetic field. X-rays and neutrons are an ideal tool for studying these materials, as they probe the characteristic energy scales and excitations that are hallmarks of these exotic quantum states. In addition to exploring Kitaev magnetism on the traditional honeycomb lattice, this program will also search for signatures of Kitaev magnetism in new families of materials based on different crystal structures and bond geometries. In this way, we hope to learn more about the fundamental properties of these Kitaev materials, and discover new design strategies to produce materials for use in quantum devices and technology.