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1. Proximity-enhanced valley Zeeman splitting at the WS 2 /graphene interface

   https://doi.org/10.1088/2053-1583/acd5df  

   Faria Junior, Paulo E. ; Naimer, Thomas ; McCreary, Kathleen M. ; Jonker, Berend T. ; Finley, Jonathan J. ; Crooker, Scott A. ; Fabian, Jaroslav ; Stier, Andreas V. ( May 2023 , 2D Materials)

   The valley Zeeman physics of excitons in monolayer transition metal dichalcogenides provides valuable insight into the spin and orbital degrees of freedom inherent to these materials. Being atomically-thin materials, these degrees of freedom can be influenced by the presence of adjacent layers, due to proximity interactions that arise from wave function overlap across the 2D interface. Here, we report 60 T magnetoreflection spectroscopy of the A- and B- excitons in monolayer WS₂, systematically encapsulated in monolayer graphene. While the observed variations of the valley Zeeman effect for the A- exciton are qualitatively in accord with expectations from the bandgap reduction and modification of the exciton binding energy due to the graphene-induced dielectric screening, the valley Zeeman effect for the B- exciton behaves markedly different. We investigate prototypical WS₂/graphene stacks employing first-principles calculations and find that the lower conduction band of WS₂at the$K/K^{\mathrm{\prime }}$valleys (the${\mathrm{C}\mathrm{B}}^{-}$band) is strongly influenced by the graphene layer on the orbital level. Specifically, our detailed microscopic analysis reveals that the conduction band at theQpoint of WS₂mediates the coupling between${\mathrm{C}\mathrm{B}}^{-}$and graphene due to resonant energy conditions and strong coupling to the Dirac cone. This leads to variations in the valley Zeeman physics of the B- exciton, consistent with the experimental observations. Our results therefore expand the consequences of proximity effects in multilayer semiconductor stacks, showing that wave function hybridization can be a multi-step energetically resonant process, with different bands mediating the interlayer interactions. Such effects can be further exploited to resonantly engineer the spin-valley degrees of freedom in van der Waals and moiré heterostructures.

    

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2. Daily Cropland Soil NO x Emissions Identified by TROPOMI and SMAP

   https://doi.org/10.1029/2020GL089949  

   Huber, Daniel E. ; Steiner, Allison L. ; Kort, Eric A. ( November 2020 , Geophysical Research Letters)

   We use TROPOMI (TROPOspheric Monitoring Instrument) tropospheric nitrogen dioxide (NO₂) measurements to identify cropland soil nitrogen oxide (NO_x = NO + NO₂) emissions at daily to seasonal scales in the U.S. Southern Mississippi River Valley. Evaluating 1.5 years of TROPOMI observations with a box model, we observe seasonality in local NO_xenhancements and estimate maximum cropland soil NO_xemissions (15–34 ng N m⁻² s⁻¹) early in growing season (May–June). We observe soil NO_xpulsing in response to daily decreases in volumetric soil moisture (VSM) as measured by the Soil Moisture Active Passive (SMAP) satellite. Daily NO₂enhancements reach up to 0.8 × 10¹⁵ molecules cm⁻²4–8 days after precipitation when VSM decreases to ~30%, reflecting emissions behavior distinct from previously defined soil NO_xpulse events. This demonstrates that TROPOMI NO₂observations, combined with observations of underlying process controls (e.g., soil moisture), can constrain soil NO_xprocesses from space.

    

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3. Distinguishing multi-decadal, quasi-periodic autogenic processes from external forcings in deltaic stratigraphy

   Pavano, F. ( December 2021 , AGU Fall Meeting)

   Periodic external environmental forcings, typically operating at Milankovitch frequencies, are known to be encoded in sediments and sedimentary rocks, but sub-Milankovitch frequencies are more difficult to recognize, in part because of temporal overlap with autogenic processes. Here we use luminescence geochronology and rock-magnetic and lithostratigraphic-based cyclostratigraphy to investigate sub-Milankovitch periodicity in three high sedimentation rate deltas located in diverse tectonic and climatic settings. The Sciota kame delta in tectonically stable eastern Pennsylvania (USA) was deposited at a rate of ~2.5 cm/yr over ~1 kyrs and has a concentration of magnetic spectral power at ~53 cm, corresponding to a ~22 yr period. Lacking a subaerial fluvial catchment, periodicity in this delta is necessarily restricted to depositional processes or ice-wasting discharge fluctuations. Similarly, the Provo-stage Lake Bonneville High Creek delta (Utah, USA) was deposited at a rate of ~3 cm/yr over ~3 kyrs. It displays meter-scale coarsening-up bedsets interpreted as decadal-scale discharge variations during foreset propagation. Unlike the Sciota kame, the High Creek delta is fed by a subaerial catchment with little storage that supported a small cirque glacier during the LGM. The High Creek delta also aggraded in the subsiding hanging wall of the East Cache Valley fault and experienced at least one syn-depositional earthquake. Lastly, The Pagliara delta (northeast Sicily, Italy) was deposited at a rate of ~3 cm/yr in the rapidly uplifting footwall of a coastal seismogenic normal fault. This delta has a concentration of magnetic susceptibility spectral power at ~60 cm corresponding to a ~20 yr period. A multi-decadal periodicity emerges in all three deltas, despite the variable catchment, climate, and tectonic setting. We interpret this as representing a quasi-periodic, autogenic depositional process possibly related to distributary channel switching. However, differences in the rock-magnetic power spectra and lithostratigraphy of the Pagliara and High Creek deltas respectfully, indicates that sub-Milankovitch external forcings in the catchments, including tectonics, are also encoded in the delta stratigraphy. 

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4. Dramatically Enhanced Valley‐Polarized Emission by Alloying and Electrical Tuning of Monolayer WTe 2 x S 2(1‐ x ) Alloys at Room Temperature with 1T′‐WTe 2 ‐Contact

   https://doi.org/10.1002/advs.202304890  

   Lin, Wei‐Hsiang ; Li, Chia‐Shuo ; Wu, Chih‐I ; Rossman, George R. ; Atwater, Harry A. ; Yeh, Nai‐Chang ( November 2023 , Advanced Science)

   Monolayer ternary tellurides based on alloying different transition metal dichalcogenides (TMDs) can result in new two‐dimensional (2D) materials ranging from semiconductors to metals and superconductors with tunable optical and electrical properties. Semiconducting WTe_2xS_2(1‐x)monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with circularly polarized light (CPL). The degree of valley polarization (DVP) under the excitation of CPL represents the purity of valley polarized photoluminescence (PL), a critical parameter for opto‐valleytronic applications. Here, new strategies to efficiently tailor the valley‐polarized PL from semiconducting monolayer WTe_2xS_2(1‐x)at room temperature (RT) through alloying and back‐gating are presented. The DVP at RT is found to increase drastically from < 5% in WS₂to 40% in WTe_0.12S_1.88by Te‐alloying to enhance the spin‐orbit coupling. Further enhancement and control of the DVP from 40% up to 75% is demonstrated by electrostatically doping the monolayer WTe_0.12S_1.88via metallic 1T′‐WTe₂electrodes, where the use of 1T′‐WTe₂substantially lowers the Schottky barrier height (SBH) and weakens the Fermi‐level pinning of the electrical contacts. The demonstration of drastically enhanced DVP and electrical tunability in the valley‐polarized emission from 1T′‐WTe₂/WTe_0.12S_1.88heterostructures paves new pathways towards harnessing valley excitons in ultrathin valleytronic devices for RT applications.

    

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5. The EDGE-CALIFA Survey: Molecular Gas and Star Formation Activity across the Green Valley

   https://doi.org/10.3847/1538-4357/ad1387  

   Villanueva, Vicente ; Bolatto, Alberto D. ; Vogel, Stuart N. ; Wong, Tony ; Leroy, Adam K. ; Sánchez, Sebastian F. ; Levy, Rebecca C. ; Rosolowsky, Erik ; Colombo, Dario ; Kalinova, Veselina ; et al ( February 2024 , The Astrophysical Journal)

   We present a¹²CO(J= 2−1) survey of 60 local galaxies using data from the Atacama Compact Array as part of the Extragalactic Database for Galaxy Evolution: the ACA EDGE survey. These galaxies all have integral field spectroscopy from the CALIFA survey. Compared to other local galaxy surveys, ACA EDGE is designed to mitigate selection effects based on CO brightness and morphological type. Of the 60 galaxies in ACA EDGE, 36 are on the star formation main sequence, 13 are on the red sequence, and 11 lie in the “green valley” transition between these sequences. We test how star formation quenching processes affect the star formation rate (SFR) per unit molecular gas mass, SFE_mol= SFR/M_mol, and related quantities in galaxies with stellar masses 10 ≤ log[M_⋆/M_⊙] ≤ 11.5 covering the full range of morphological types. We observe a systematic decrease of the molecular-to-stellar mass fraction ($R_{\star }^{\mathrm{mol}}$) with a decreasing level of star formation activity, with green valley galaxies also having lower SFE_molthan galaxies on the main sequence. On average, we find that the spatially resolved SFE_molwithin the bulge region of green valley galaxies is lower than in the bulges of main-sequence galaxies if we adopt a constant CO-to-H₂conversion factor,α_CO. While efficiencies in main-sequence galaxies remain almost constant with galactocentric radius, in green valley galaxies, we note a systematic increase of SFE_mol,$R_{\star }^{\mathrm{mol}}$, and specific SFR with increasing radius. As shown in previous studies, our results suggest that although gas depletion (or removal) seems to be the most important driver of the star formation quenching in galaxies transiting through the green valley, a reduction in star formation efficiency is also required during this stage.

    

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