Non-technical abstract: “Quantum materials” are those which have unusual properties arising from the quantum mechanical nature of electrons in solids. In quantum magnets, it is the spin of the electrons which are engaged in this quantum behavior. Quantum magnets often host wildly dynamic spins at very low temperatures, and can be manipulated to form new quantum phases of matter under various conditions, such as in a strong applied magnetic field. Through this project, new quantum magnetic materials are synthesized and studied in such extreme environments, with the goal of finding new quantum magnetic phenomena, like a quantum spin liquid. The materials studied here are based on rare-earth elements, which have traditionally been overlooked as key ingredients for quantum magnets, but in reality give a much wider range of possibilities for quantum behavior compared to traditional materials design approaches. This work focuses on rare-earth based materials in which the spins are arranged into a graphene-like geometry called the honeycomb lattice. The magnetic behavior of these materials is explored in detail using a wide range of advanced techniques, such as neutron scattering. This project advances the understanding of quantum many-body systems and highlights new ways in which they can be realized in nature. It also contributes to the training of highly qualified personnel in the methods of materials synthesis and characterization. The training of the future generation of materials scientists, particularly those well-versed in quantum phenomena, is essential for future paradigm-shifting advances in materials research.

Technical Abstract

Rare-earth based honeycomb lattice materials are an unconventional class of quantum magnets. Due to the presence of strongly quantum fluctuating spins, in combination with anisotropic interactions arising from strong spin-orbit coupling, these materials can host a different set of quantum phases than can be achieved in traditional (3d transition-metal based) quantum magnets. This project will investigate a range of phenomena which have been found to manifest in rare-earth based honeycomb lattice materials, including quantum dimer magnetism leading to field-induced Bose Einstein condensation, Ising-like quantum criticality, and promising avenues to realize the highly entangled Kitaev quantum spin liquid. The project involves the synthesis of bulk samples of rare-earth honeycomb materials, with particular emphasis on single-crystal growth. These materials are characterized by thermodynamic probes and inelastic neutron scattering. Thermodynamics gives a road map of the phase diagrams, while inelastic neutron scattering enables the understanding of the emergent quasi-particle excitations and their evolution with varying applied magnetic field. The relatively weak interaction energies of rare-earth materials enables the use of a powerful method of determining the interaction parameters in these materials, via theoretical modeling of field-polarized inelastic neutron scattering spectra. This work has relevance to a broad range of other areas of physics research, such as superfluid helium in porous media, superconductivity, and ultra-cold atomic gases. The impacts of this work also extend beyond many-body quantum physics; through this project, students who are part of underrepresented minority groups in physics, are encouraged to explore the concept of magnetism and phase transitions in materials and to gain hands-on research experience.

This Division of Materials Research (DMR) grant supports research to understand a range of phenomena which have been found to manifest in rare-earth based honeycomb lattice materials with funding from the Condensed Matter Physics (CMP) Program in DMR of the Mathematical and Physical Sciences Directorate.

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.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Tom Oder
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Colorado State University-Fort Collins
Fort Collins
United States
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