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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. Free, publicly-accessible full text available July 18, 2023
  3. Free, publicly-accessible full text available July 10, 2023
  4. 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
  5. As work changes, so does technology. The two coevolve as part of a work ecosystem. This paper suggests a way of plotting this coevolution by comparing the embeddings - high dimensional vector representations - of textual descriptions of tasks, occupations and technologies. Tight coupling between tasks and technologies - measured by the distances between vectors - are shown to be associated with high task importance. Moreover, tasks that are more prototypical in an occupation are more important. These conclusions were reached through an analysis of the 2020 data release of The Occupational Information Network (O*NET) from the U.S. Department ofmore »Labor on 967 occupations and 19,533 tasks. One occupation, journalism, is analyzed in depth, and conjectures are formed related to the ways technologies and tasks evolve through both design and exaptation.« less
    Free, publicly-accessible full text available January 1, 2023
  6. Free, publicly-accessible full text available December 1, 2022
  7. Abstract We report a timing analysis of near-infrared (NIR), X-ray, and submillimeter data during a 3 day coordinated campaign observing Sagittarius A*. Data were collected at 4.5 μ m with the Spitzer Space Telescope, 2–8 keV with the Chandra X-ray Observatory, 3–70 keV with NuSTAR, 340 GHz with ALMA, and 2.2 μ m with the GRAVITY instrument on the Very Large Telescope Interferometer. Two dates show moderate variability with no significant lags between the submillimeter and the infrared at 99% confidence. A moderately bright NIR flare ( F K ∼ 15 mJy) was captured on July 18 simultaneous with anmore »X-ray flare ( F 2−10 keV ∼ 0.1 counts s −1 ) that most likely preceded bright submillimeter flux ( F 340 GHz ∼ 5.5 Jy) by about + 34 − 33 + 14 minutes at 99% confidence. The uncertainty in this lag is dominated by the fact that we did not observe the peak of the submillimeter emission. A synchrotron source cooled through adiabatic expansion can describe a rise in the submillimeter once the synchrotron self-Compton NIR and X-ray peaks have faded. This model predicts high GHz and THz fluxes at the time of the NIR/X-ray peak and electron densities well above those implied from average accretion rates for Sgr A*. However, the higher electron density postulated in this scenario would be in agreement with the idea that 2019 was an extraordinary epoch with a heightened accretion rate. Since the NIR and X-ray peaks can also be fit by a nonthermal synchrotron source with lower electron densities, we cannot rule out an unrelated chance coincidence of this bright submillimeter flare with the NIR/X-ray emission.« less
    Free, publicly-accessible full text available May 1, 2023
  8. Free, publicly-accessible full text available March 1, 2023
  9. 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