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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
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  6. A thermoelectric building envelope (TBE) is a new type of active building envelope that incorporates thermoelectric material in the building’s enclosure. In TBE, the electrical energy and thermal energy can transfer between them through thermoelectric material. TBE can provide cooling or heating to indoor space if power is applied. TBE-based cooling or heating is quiet and reliable and has low maintenance cost, low or no CO2 emission. TBE is conducive to the operation of net-zero energy and emission buildings by using renewable and low-grade energy. In this study, a multi-stage TBE prototype was designed, assembled, and tested. The performance ofmore »the TBE prototype was evaluated in two psychrometric chambers with controlled temperature and humidity in Herrick Laboratory at Purdue University. The test result concludes that the highest COP of TBE is 0.46–2.4 in summer scenarios for different power inputs. The findings discussed can guide the design and operation of TBE.« less
    Free, publicly-accessible full text available September 8, 2022
  7. Thermoelectric (TE) cement composite is a new type of TE material. Unlike ordinary cement, due to the inclusion of additives, TE cement can mutually transform thermal energy into electrical energy. In extreme weather, the large temperature difference between indoor and outdoor can be harvested by TE cement to generate electricity. In moderate weather, given power input, the same material can provide cooling/heating to adjust room temperature and reduce HAVC load. Therefore, TE cement has energy-saving potential in the application of building enclosures and energy systems. Its ability to convert different forms of energy and use low-grade energy is conducive tomore »the operation of net-zero buildings. In this study, the graphene nanoplatelets and aluminum-doped zinc oxide nanopowder enhanced cement composite, was fabricated. The performance indicator of TE materials includes the dimensionless figure of merit ZT, calculated by Seebeck coefficient, thermal conductivity, and electrical conductivity. These TE properties were measured and calculated by a Physical Property Measurement System at different temperatures. The highest ZT of 15wt.% graphene and 5wt.% AZO enhanced cement composite prepared by the dry method is about 5.93E-5 at 330K.« less
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