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1. Tropical forests are facing increasing risks of exposure to critical temperature thresholds

   https://doi.org/10.1073/pnas.2528622123  

   van_Tiel, Nina; Lenczner, Gaston; Rao, Mukund P; Grossiord, Charlotte; Tuia, Devis (July 2026, Proceedings of the National Academy of Sciences)

   Understanding how close tropical tree species are to critical temperature thresholds that might impede photosynthetic activity is vital in a world where heat waves have become more severe and frequent. Using remotely sensed surface temperature and species distribution maps, we studied the spatiotemporal variation in the thermal safety margins (TSM, i.e., the difference between $T_{\text{crit}}$ , the critical photosynthetic temperature, and the maximum canopy temperature) of $208$ tropical tree species in South America, Southeast Asia, and Central Africa during the period 2001–2020. Despite overall high-temperature tolerance with an average $T_{\text{crit}}$ of $46.1{}^{°}$ C, we observed a consistent decline in the TSM of tropical forests across the globe. The average pantropical TSM decline was $0.4{}^{°}$ C per decade, with the strongest decline in South America ( $0.5{}^{°}$ C per decade). Over the $20$ -y period, areas that experienced canopy temperatures surpassing the average $T_{\text{crit}}$ across reported species increased from $43$ Mha to $57$ Mha in the tropics, representing $4\%$ of the studied area. This number increases to $10\%$ when computing areas where temperatures have surpassed the $T_{\text{crit}}$ of the most vulnerable reported species. When considering future trends, as predicted by Earth System Models under medium-to-high emission scenarios, average $T_{\text{crit}}$ may be exceeded in an area of $83$ Mha by $2050$ and $160$ Mha by $2100$ (over $10\%$ of the studied area), suggesting major feedback to the global carbon cycle and the world’s biodiversity. 

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2. Designing multicomponent hydrides with potential high T _c superconductivity

   https://doi.org/10.1073/pnas.2413096121  

   Denchfield, Adam; Park, Hyowon; Hemley, Russell J (November 2024, Proceedings of the National Academy of Sciences)

   While hydrogen-rich materials have been demonstrated to exhibit high T_csuperconductivity at high pressures, there is an ongoing search for ternary, quaternary, and more chemically complex hydrides that achieve such high critical temperatures at much lower pressures. First-principles searches are impeded by the computational complexity of solving the Eliashberg equations for large, complex crystal structures. Here, we adopt a simplified approach using electronic indicators previously established to be correlated with superconductivity in hydrides. This is used to study complex hydride structures, which are predicted to exhibit promisingly high critical temperatures for superconductivity. In particular, we propose three classes of hydrides inspired by the Fm $\overline{3}$ m RH ${}_3$ structures that exhibit strong hydrogen network connectivity, as defined through the electron localization function. The first class [RH ${}_{11}$ X ${}_3$ Y] is based on a Pm $\overline{3}$ m structure showing moderately high T_c, where the T_cestimate from electronic properties is compared with direct Eliashberg calculations and found to be surprisingly accurate. The second class of structures [(RH ${}_{11}$ ) ${}_2$ X ${}_6$ YZ] improves on this with promisingly high density of states with dominant hydrogen character at the Fermi energy, typically enhancing T_c. The third class [(R ${}^1$ H ${}_{11}$ )(R ${}^2$ H ${}_{11}$ )X ${}_6$ YZ] improves the strong hydrogen network connectivity by introducing anisotropy in the hydrogen network through a specific doping pattern. These design principles and associated model structures provide flexibility to optimize both T_cand the structural stability of complex hydrides. 

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3. Massive Extremely High-velocity Outflow in the Quasar J164653.72+243942.2

   https://doi.org/10.3847/1538-4357/adef0d  

   Rodríguez_Hidalgo, Paola; Choi_최, Hyunseop 현섭; Hall, Patrick B; Leighly, Karen M; Flores, Liliana; Charles, Mikel M; DeFrancesco, Cora; Hlavacek-Larrondo, Julie; Perreault-Levasseur, Laurence (September 2025, The Astrophysical Journal)

   Abstract We present analysis of one of the most extreme quasar outflows found to date in our survey of extremely high-velocity outflows (EHVOs). J164653.72+243942.2 (z_em ∼ 3.04) shows variable Civλλ1548,1551 absorption at speeds larger than 0.1c, accompanied by Siiv, Nv,and Lyα, and disappearing absorption at lower speeds. We perform absorption measurements using the apparent optical depth method and SimBAL. We find the absorption to be very broad (Δv ∼  35,100 km s⁻¹in the first epoch and 13,000 km s⁻¹in the second one) and fast (v_max ∼  –50,200 km s⁻¹and −49,000 km s⁻¹, respectively). We measure large column densities ( $\log N_{\mathrm{H}}>$ 21.6 (cm⁻²)) and are able to place distance estimates for the EHVO (5 ≲ R ≲ 28 pc) and the lower-velocity outflow (7 ≲ R ≲ 540 pc). We estimate a mass outflow rate for the EHVO to be ${\dot{M}}_{\mathrm{out}}\sim 50–290M_{\odot }{\mathrm{yr}}^{-1}$ and a kinetic luminosity of $\log L_{\mathrm{KE}}\sim 46.5–47.2\left(\mathrm{erg}{\mathrm{s}}^{-1}\right)$ in both epochs. The lower-velocity component has a mass outflow rate ${\dot{M}}_{\mathrm{out}}\sim 10–790M_{\odot }{\mathrm{yr}}^{-1}$ and a kinetic luminosity of $\log L_{\mathrm{KE}}\sim 45.3–47.2\left(\mathrm{erg}{\mathrm{s}}^{-1}\right)$ . We find that J164653.72+243942.2 is not an outlier among EHVO quasars in regard to its physical properties. While its column density is lower than typical BAL values, its higher outflow velocities drive most of the mass outflow rate and kinetic luminosity. These results emphasize the crucial role of EHVOs in powering quasar feedback, and failing to account for these outflows likely leads to underestimating the feedback impact on galaxies. 

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4. Measurement of the dynamic charge susceptibility near the charge density wave transition in ErTe ₃

   https://doi.org/10.1073/pnas.2424430122  

   Chaudhuri, Dipanjan; Jiang, Qianni; Guo, Xuefei; Chen, Jin; Kengle, Caitlin S; Hoveyda-Marashi, Farzaneh; Bernal-Choban, Camille; de_Vries, Niels; Chiang, Tai-Chang; Fradkin, Eduardo; et al (June 2025, Proceedings of the National Academy of Sciences)

   A charge density wave (CDW) is a phase of matter characterized by a periodic modulation of valence electron density coupled with lattice distortion. Its formation is closely tied to the dynamical charge susceptibility, $\chi (q,\omega )$ , which reflects the collective electron dynamics of the material. Despite decades of study, $\chi (q,\omega )$ near a CDW transition has never been measured at nonzero momentum, $q$ , with meV energy resolution. Here, we investigate the canonical CDW transition in ErTe ${}_3$ using momentum-resolved electron energy loss spectroscopy, a technique uniquely sensitive to valence band charge excitations. Unlike phonons, which soften via the Kohn anomaly, we find the electronic excitations exhibit purely relaxational dynamics well described by a diffusive model, with the diffusivity peaking just below the critical temperature, $T_{C1}$ . Additionally, we report for the first time a divergence in the real part of $\chi (q,\omega )$ in the static limit ( $\omega \to 0$ ), a long-predicted hallmark of CDWs. Unexpectedly, this divergence occurs as $T\to 0$ , with only a weak thermodynamic signature at $T=T_{C1}$ . Our study necessitates a reexamination of the traditional description of CDW formation in quantum materials. 

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5. ASPIRE: The Environments and Dark Matter Halos of Luminous Quasars in the Epoch of Reionization

   https://doi.org/10.3847/1538-4357/ae7bfa  

   Wang, Feige; Champagne, Jaclyn B; Huang, Jiamu; Yang, Jinyi; Hennawi, Joseph F; Fan, Xiaohui; Zhang, Haowen; Costa, Tiago; Decarli, Roberto; Habouzit, Melanie; et al (July 2026, The Astrophysical Journal)

   Abstract We present a systematic study of the environments of 25 luminous quasars atz > 6.5 from the ASPIRE program. Using JWST/NIRCam wide-field slitless spectroscopy data, we identified 487 galaxies at 5.3 ≲ z ≲ 7.0 exhibiting [Oiii] emission. Among these, 122 [Oiii] emitters lie within ∣Δv_los∣ < 1000 km s⁻¹of the quasars, corresponding to a ∼9.4-fold enhancement relative to the average galaxy density at other redshifts. Furthermore, we identified 16 [Cii]-emitting galaxies at the quasar redshifts from Atacama Large Millimeter/submillimeter Array (ALMA) mosaic observations. A cross-correlation function analysis between quasars and [Oiii]+[Cii] emitters yields a cross-correlation length of $r_0^{\mathrm{QG}}=8.68_{-0.55}^{+0.51}{h}^{-1}\mathrm{cMpc}$ and an autocorrelation of $r_0^{\mathrm{QQ}}=15.76_{-2.70}^{+2.48}{h}^{-1}\mathrm{cMpc}$ , indicating thatz ∼ 7 quasars reside in dark matter halos with $M_{\mathrm{halo}}=10^{12.27_{-0.26}^{+0.21}}{M}_{\odot }$ and have a quasar lifetime of $t_Q=10^{{7.05}_{-1.01}^{+0.95}}\mathrm{yr}$ . Notably, the number of [Oiii]-emitting galaxies at quasar redshifts varies significantly from field to field, ranging from 0 to 20, highlighting a diverse quasar environment. Remarkably, seven quasars trace significant galaxy overdensities (i.e., protoclusters), withδ_gal > 5 within a volume ofV ∼ 500 cMpc³. We also find that ∣Δv_los∣ increases rapidly toward smaller galaxy–quasar separations in protocluster fields, consistent with galaxy kinematics around extremely massive halos in cosmological simulations. By combining JWST and ALMA data, we reveal the complex and diverse environments of these early quasars, providing robust evidence that the earliest luminous quasars are effective tracers of galaxy overdensities, albeit with substantial field-to-field variation. 

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