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  1. Abstract Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spin-singlet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr 3 Ir 2 O 7 . By isolating the longitudinal component of the spectra, we identify a magnetic mode that is well-defined at the magnetic and structural Brillouin zone centers, but which merges withmore »the electronic continuum in between these high symmetry points and which decays upon heating concurrent with a decrease in the material’s resistivity. We show that a bilayer Hubbard model, in which electron-hole pairs are bound by exchange interactions, consistently explains all the electronic and magnetic properties of Sr 3 Ir 2 O 7 indicating that this material is a realization of the long-predicted antiferromagnetic excitonic insulator phase.« less
    Free, publicly-accessible full text available December 1, 2023
  2. The search for quantum spin liquids – topological magnets with fractionalized excitations – has been a central theme in condensed matter and materials physics. Despite numerous theoretical proposals, connecting experiment with detailed theory exhibiting a robust quantum spin liquid has remained a central challenge. Here, focusing on the strongly spin-orbit coupled effective S=1/2 pyrochlore magnet Ce2Zr2O7, we analyse recent thermodynamic and neutron scattering experiments, to identify a microscopic effective Hamiltonian through a combination of finite temperature Lanczos, Monte Carlo and analytical spin dynamics calculations. Its parameter values suggest the existence of an exotic phase, a pi-flux U(1) quantum spin liquid.more »Intriguingly, the octupolar nature of the moments makes them less prone to be affected by magnetic disorder, while also hiding some otherwise characteristic signatures from neutrons, making this spin liquid arguably more stable than its more conventional counterparts.« less
    Free, publicly-accessible full text available May 2, 2023
  3. Free, publicly-accessible full text available December 1, 2022
  4. This paper introduces the background and establishment of the first Research Experience for Teachers (RET) Site in Arkansas, supported by the National Science Foundation. The Arkansas Data Analytics Teacher Alliance (AR-DATA) program partners with school districts in the Northwest Arkansas region to promote research-driven high school analytics curriculum and education to reach underserved students, such as those from rural areas. At least thirty 9th-12th grade mathematics, computer science, and pre-engineering teachers will participate in AR-DATA and work with faculty mentors, graduate students, curriculum coaches, and industry experts in a six-week RET Summer Program and academic-year follow up to develop andmore »disseminate learning modules to enhance current curriculum, attain new knowledge of data analytics and engineering applications, and benefit professionally through the RET program activities. The learning modules developed will reflect current cutting-edge analytics research, as well as the development needs of next-generation analytics workforce.« less
    Free, publicly-accessible full text available September 13, 2022
  5. Two-dimensional van der Waals (vdWs) materials have gathered a lot of attention recently. However, the majority of these materials have Curie temperatures that are well below room temperature, making it challenging to incorporate them into device applications. In this work, we synthesized a room-temperature vdW magnetic crystal Fe5GeTe2 with a Curie temperature T$_c = 332$ K, and studied its magnetic properties by vibrating sample magnetometry (VSM) and broadband ferromagnetic resonance (FMR) spectroscopy. The experiments were performed with external magnetic fields applied along the c-axis (H$\parallel$c) and the ab-plane (H$\parallel$ab), with temperatures ranging from 300 to 10 K. We have foundmore »a sizable Landé g-factor difference between the H$\parallel$c and H$\parallel$ab cases. In both cases, the Landé g-factor values deviated from g = 2. This indicates contribution of orbital angular momentum to the magnetic moment. The FMR measurements reveal that Fe5GeTe2 has a damping constant comparable to Permalloy. With reducing temperature, the linewidth was broadened. Together with the VSM data, our measurements indicate that Fe5GeTe2 transitions from ferromagnetic to ferrimagnetic at lower temperatures. Our experiments highlight key information regarding the magnetic state and spin scattering processes in Fe5GeTe2, which promote the understanding of magnetism in Fe5GeTe2, leading to implementations of Fe5GeTe2 based room-temperature spintronic devices.« less
    Free, publicly-accessible full text available September 13, 2022
  6. Free, publicly-accessible full text available June 1, 2022