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The Arctic climate is sensitive to aerosol abundance, making accurate historical records of atmospheric aerosols essential for understanding the recent rapid Arctic warming. We present 235-year ice core records of sulfate (SO42-), nitrate (NO3-), chloride (Cl-) and other impurities from central Greenland, and compare them with emission inventories in the surrounding continents. The comparisons reveal a high correlation between the ice core records and North American emissions, consistent with that North America as the dominant pollution source region to Greenland. Since around 1970, SO42-, NO3- and Cl- exhibit divergent patterns relative to their pre-1970 increasing trends paralleling with anthropogenic emissions. In particular, SO42- declined in step with North American SO2 emissions but decreased more rapidly after ~1990, probably due to combined effects from the enhanced sulfate loss in the source regions due to intensified in-cloud sulfur oxidation and the reduced transport efficiency. Nitrate tracked NOX emissions since ~ 1900 until 1990, but remained high after 1990 when anthropogenic emissions in all source regions decreased. This post-1990 pattern may arise from the increasing natural NOX emissions in the Arctic, while feedbacks of atmospheric chemistry to a changing atmospheric acidity during this period may also contribute through affecting the phase partitioning and then long-range transport of nitrate. Chloride also paralleled with anthropogenic emissions since the 1960s but was further modulated by acid displacement processes, as indicated by the covariation of Cl- excess with reconstructed snow acidity. Our results demonstrate that Arctic aerosols reflect both emission controls and their modulation by atmospheric chemistry and transport. 

Silicon’s indirect band gap severely suppresses radiative recombination, limiting its use as an efficient light-emitting material. Although nanoscale confinement of carriers, dielectric resonators, or plasmonic structures can partially mitigate this limitation, these approaches typically require complex fabrication. Here, we report a fundamentally different and scalable mechanism that enables efficient light emission directly from bulk silicon. By decorating a silicon wafer with ultrasmall (<2 nm) gold or copper particles, we observe intense luminescence spanning the visible and near-infrared. Remarkably, the emission is indistinguishable for Au and Cu decorations in both spectral and temporal domains, demonstrating that the confinement extent, not the material composition, governs the effect. We attribute the emission to spatially confined photonic states with broadened momentum distributions, enabling phonon-independent optical transitions otherwise forbidden in silicon. This mechanism yields quantum efficiencies comparable to those of direct-band-gap semiconductors and produces ∼a 10^5-fold enhancement in the integrated emission intensity, establishing a practical route toward silicon light-emitting devices. 

Abstract Single-particle continuum models such as the popular Bistritzer–MacDonald model have become powerful tools for predicting electronic phenomena of incommensurate 2D materials and developing many-body models aimed at modeling unconventional superconductivity and correlated insulators. In this work, we introduce a procedure to construct continuum models of arbitrary accuracy relative to tight-binding models for moiré incommensurate bilayers. This is done by recognizing the continuum model as arising from Taylor expansions of a high accuracy momentum space approximation of the tight-binding model. We apply our procedure in full detail to two models of twisted bilayer graphene and demonstrate both admit similar Bistritzer–MacDonald models as the leading order continuum model, while higher order expansions reveal qualitative spectral differences. 

Abstract Twisted bilayer graphene (TBG) has drawn significant interest due to recent experiments which show that TBG can exhibit strongly correlated behavior such as the superconducting and correlated insulator phases. Much of the theoretical work on TBG has been based on analysis of the Bistritzer–MacDonald model which includes a phenomenological parameter to account for lattice relaxation. In this work, we use a newly developed continuum model which systematically accounts for the effects of structural relaxation. In particular, we model structural relaxation by coupling linear elasticity to a stacking energy that penalizes disregistry. We compare the impact of the two relaxation models on the corresponding many-body model by defining an interacting model projected to the flat bands. We perform tests at charge neutrality at both the Hartree–Fock and coupled cluster singles and doubles level of theory and find the systematic relaxation model gives quantitative differences from the simplified relaxation model. 

The first-order continuum partial differential equation (PDE) model proposed by Bistritzer and MacDonald [Proc. Natl. Acad. Sci. U. S. A. 108, 12233–12237 (2011)] accurately describes the single-particle electronic properties of twisted bilayer graphene at small twist angles. In this paper, we obtain higher-order corrections to the Bistritzer–MacDonald (BM) model via a systematic multiple-scales expansion. We prove that the solution of the resulting higher-order PDE model accurately approximates the corresponding tight-binding wave function under a natural choice of parameters and given initial conditions that are spectrally localized to the monolayer Dirac points. Numerical simulations of tight-binding and continuum dynamics demonstrate the validity of the higher-order continuum model. Symmetries of the higher-order models are also discussed. This work extends the analysis from Watson et al., J. Math. Phys. 64, 031502 (2023), which rigorously established the validity of the (first-order) BM model.