Quenched Disorder in Frustrated Magnets

University Of California-Davis, Davis CA

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports research and education on theoretical and computational modeling of the properties of magnetic materials, where quantum mechanics plays a central role. Magnetism is a phenomenon associated with the electron's tiny intrinsic magnetic moment, called spin. In the best-known magnetic materials, such as iron, electrons in the material have their spins lined up parallel to each other and produce magnetic fields at macroscopic scales. We experience these through their magnetic forces. In another class of magnetic materials, spins line up anti-parallel with their neighbors. Such materials do not exhibit macroscopic magnetic forces, but their behavior can still be understood within a classical framework. Frustration in the context of magnetism is a technical term that denotes the existence of competing forces at the microscopic level. Frustration can destabilize any arrangement of spin order and lead to far more complex behavior. Quantum mechanics is essential for describing such magnetic phases. Materials having these magnetic phases can harbor new types of particles and show new types of responses to temperature changes, electric current, or electromagnetic fields. They could provide platforms for a new generation of quantum devices. In recent years, many such quantum magnetic materials have been synthesized and are being studied. However, real materials always come with imperfections or impurities. Such impurities can sometimes degrade and sometimes stabilize exotic properties. This project seeks to understand in detail the role of impurities in frustrated magnetism. In addition to their scientific value to the understanding of exotic quantum materials and technologies, these studies also provide excellent training ground for undergraduate and graduate students in theoretical and computational methods. TECHNICAL SUMMARY This award supports research and education on the role of quenched disorder in frustrated magnets using theoretical and computational methods. The quest for exotic quantum spin-liquid phases of matter is poised at an interesting juncture. Several families of magnetic materials have been synthesized that exhibit absence of conventional magnetic order. A theoretical framework is in place for understanding quantum spin-liquid phases of matter that includes exactly solvable models and emergent gauge theories. In parallel, computational methods have been developed that can address realistic quantum spin models needed to study quantitative macroscopic properties of such materials. This project will address such quantum spin models with quenched impurities by a number of theoretical and computational techniques. These techniques include series expansions and numerical linked cluster expansions developed by the PI and his group. By calculating thermodynamic properties such as entropy and specific heat, dynamical properties such as spin-currents and spin-diffusion, and various response and scattering properties, the work should provide quantitative support to various experimental studies including transport, neutron scattering and NMR experiments. These studies should help develop a comprehensive understanding of these class of materials and prepare them for their possible use in next-generation quantum technologies. In addition to their scientific value to the understanding of exotic quantum materials and technologies, these studies also provide excellent training ground for undergraduate and graduate students in theoretical and computational methods. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.