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Mazzone, D. G.; Shen, Y.; Suwa, H.; Fabbris, G.; Yang, J.; Zhang, S.-S.; Miao, H.; Sears, J.; Jia, Ke; Shi, Y. G.; et al(
, Nature Communications)
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
We present a multiline survey of the interstellar medium (ISM) in two z > 6 quasar host galaxies, PJ231−20 ( z = 6.59) and PJ308−21 ( z = 6.23), and their two companion galaxies. Observations were carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted 11 transitions including atomic fine-structure lines (FSLs) and molecular lines: [NII] 205 μm , [CI] 369 μm , CO ( J up = 7, 10, 15, 16), H 2 O 3 12 − 2 21 , 3 21 − 3 12 , 3 03 − 2 12 , and the OH 163 μm doublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respectivemore »dust emission. By combining this information with our earlier ALMA [CII] 158 μm observations, we explored the effects of star formation and black hole feedback on the ISM of the galaxies using the CLOUDY radiative transfer models. We estimated dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the [CII] 158 μm and [CI] 369 μm emission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits agree with those of local luminous IR galaxies. The CO spectral line energy distributions (SLEDs) reveal significant high- J CO excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231−20 shows that PDRs dominate the molecular mass and CO luminosities for J up ≤ 7, while the J up ≥ 10 CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host. The J up > 10 lines are undetected in the other galaxies in our study. The H 2 O 3 21 − 3 12 line detection in the same quasar places this object on the L H 2 O − L TIR relation found for low- z sources, thus suggesting that this water vapor transition is predominantly excited by IR pumping. Models of the H 2 O SLED and of the H 2 O-to-OH 163 μm ratio point to PDR contributions with high volume and column density ( n H ∼ 0.8 × 10 5 cm −3 , N H = 10 24 cm −2 ) in an intense radiation field. Our analysis suggests a less highly excited medium in the companion galaxies. However, the current data do not allow us to definitively rule out an AGN in these sources, as suggested by previous studies of the same objects. This work demonstrates the power of multiline studies of FIR diagnostics in order to dissect the physical conditions in the first massive galaxies emerging from cosmic dawn.« less
Free, publicly-accessible full text available August 1, 2022
Park, N.; Ryu, H.; Ding, Y.; Yu, Q.; Bu, Y.; Wang, Q.; Yang, J.; & Song, M.(
, The 18th International Conference on Scientometrics and Informetrics, Leuven, Belgium, July 12-15, 2021.)
Yang, J.; Wang, Y.; Yi, R.; Zhu, Y.; Rehman, A.; Zadeh, A.; Poria, S.; Morency, L.-P.(
, Proceedings of the 17th Annual Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies (NAACL), 2021)
In plants, changes in cell size and shape during development fundamentally depend on the ability to synthesize and modify cell wall polysaccharides. The main classes of cell wall polysaccharides produced by terrestrial plants are cellulose, hemicelluloses, and pectins. Members of the cellulose synthase (CESA) and cellulose synthase-like (CSL) families encode glycosyltransferases that synthesize the β-1,4-linked glycan backbones of cellulose and most hemicellulosic polysaccharides that comprise plant cell walls. Cellulose microfibrils are the major load-bearing component in plant cell walls and are assembled from individual β-1,4-glucan polymers synthesized by CESA proteins that are organized into multimeric complexes called CESA complexes, inmore »the plant plasma membrane. During distinct modes of polarized cell wall deposition, such as in the tip growth that occurs during the formation of root hairs and pollen tubes or de novo formation of cell plates during plant cytokinesis, newly synthesized cell wall polysaccharides are deposited in a restricted region of the cell. These processes require the activity of members of the CESA-like D subfamily. However, while these CSLD polysaccharide synthases are essential, the nature of the polysaccharides they synthesize has remained elusive. Here, we use a combination of genetic rescue experiments with CSLD-CESA chimeric proteins, in vitro biochemical reconstitution, and supporting computational modeling and simulation, to demonstrate that Arabidopsis (Arabidopsis thaliana) CSLD3 is a UDP-glucose-dependent β-1,4-glucan synthase that forms protein complexes displaying similar ultrastructural features to those formed by CESA6.« less
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