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1. The Simons Observatory: Galactic Science Goals and Forecasts

   https://doi.org/10.3847/1538-4357/ac5e36  

   Hensley, Brandon S. ; Clark, Susan E. ; Fanfani, Valentina ; Krachmalnicoff, Nicoletta ; Fabbian, Giulio ; Poletti, Davide ; Puglisi, Giuseppe ; Coppi, Gabriele ; Nibauer, Jacob ; Gerasimov, Roman ; et al ( April 2022 , The Astrophysical Journal)

   Observing in six frequency bands from 27 to 280 GHz over a large sky area, the Simons Observatory (SO) is poised to address many questions in Galactic astrophysics in addition to its principal cosmological goals. In this work, we provide quantitative forecasts on astrophysical parameters of interest for a range of Galactic science cases. We find that SO can: constrain the frequency spectrum of polarized dust emission at a level of Δβ_d≲ 0.01 and thus test models of dust composition that predict thatβ_din polarization differs from that measured in total intensity; measure the correlation coefficient between polarized dust and synchrotron emission with a factor of two greater precision than current constraints; exclude the nonexistence of exo-Oort clouds at roughly 2.9σif the true fraction is similar to the detection rate of giant planets; map more than 850 molecular clouds with at least 50 independent polarization measurements at 1 pc resolution; detect or place upper limits on the polarization fractions of CO(2–1) emission and anomalous microwave emission at the 0.1% level in select regions; and measure the correlation coefficient between optical starlight polarization and microwave polarized dust emission in 1° patches for all lines of sight withN_H≳ 2 × 10²⁰cm⁻². The goals and forecasts outlined here provide a roadmap for other microwave polarization experiments to expand their scientific scope via Milky Way astrophysics.³⁷³⁷

   A supplement describing author contributions to this paper can be found athttps://simonsobservatory.org/wp-content/uploads/2022/02/SO_GS_Contributions.pdf.

    

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2. Pines’ demon observed as a 3D acoustic plasmon in Sr2RuO4

   https://doi.org/10.1038/s41586-023-06318-8  

   Husain, Ali A. ; Huang, Edwin W. ; Mitrano, Matteo ; Rak, Melinda S. ; Rubeck, Samantha I. ; Guo, Xuefei ; Yang, Hongbin ; Sow, Chanchal ; Maeno, Yoshiteru ; Uchoa, Bruno ; et al ( September 2023 , Nature)

   The characteristic excitation of a metal is its plasmon, which is a quantized collective oscillation of its electron density. In 1956, David Pines predicted that a distinct type of plasmon, dubbed a ‘demon’, could exist in three-dimensional (3D) metals containing more than one species of charge carrier¹. Consisting of out-of-phase movement of electrons in different bands, demons are acoustic, electrically neutral and do not couple to light, so have never been detected in an equilibrium, 3D metal. Nevertheless, demons are believed to be critical for diverse phenomena including phase transitions in mixed-valence semimetals², optical properties of metal nanoparticles³, soundarons in Weyl semimetals⁴and high-temperature superconductivity in, for example, metal hydrides^3,5–7. Here, we present evidence for a demon in Sr₂RuO₄from momentum-resolved electron energy-loss spectroscopy. Formed of electrons in theβandγbands, the demon is gapless with critical momentumq_c = 0.08 reciprocal lattice units and room-temperature velocityv = (1.065 ± 0.12) × 10⁵m s⁻¹that undergoes a 31% renormalization upon cooling to 30 K because of coupling to the particle–hole continuum. The momentum dependence of the intensity of the demon confirms its neutral character. Our study confirms a 67-year old prediction and indicates that demons may be a pervasive feature of multiband metals.

    

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3. Global perspectives of the bulk electronic structure of URu 2 Si 2 from angle-resolved photoemission

   https://doi.org/10.1088/2516-1075/ac4315  

   Denlinger, J. D. ; Kang, J-S ; Dudy, L. ; Allen, J. W. ; Kim, Kyoo ; Shim, J-H ; Haule, K. ; Sarrao, J. L. ; Butch, N. P. ; Maple, M. B. ( January 2022 , Electronic Structure)

   Previous high-resolution angle-resolved photoemission (ARPES) studies of URu₂Si₂have characterized the temperature-dependent behavior of narrow-band states close to the Fermi level (E_F) at low photon energies near the zone center, with an emphasis on electronic reconstruction due to Brillouin zone folding. A substantial challenge to a proper description is that these states interact with other hole-band states that are generally absent from bulk-sensitive soft x-ray ARPES measurements. Here we provide a more globalk-space context for the presence of such states and their relation to the bulk Fermi surface (FS) topology using synchrotron-based wide-angle and photon energy-dependent ARPES mapping of the electronic structure using photon energies intermediate between the low-energy regime and the high-energy soft x-ray regime. Small-spot spatial dependence,f-resonant photoemission, Si 2pcore-levels, x-ray polarization, surface-dosing modification, and theoretical surface slab calculations are employed to assist identification of bulk versus surface state character of theE_F-crossing bands and their relation to specific U- or Si-terminations of the cleaved surface. The bulk FS topology is critically compared to density functional theory (DFT) and to dynamical mean field theory calculations. In addition to clarifying some aspects of the previously measured high symmetry Γ,ZandXpoints, incommensurate 0.6a* nested Fermi-edge states located alongZ–N–Zare found to be distinctly different from the DFT FS prediction. The temperature evolution of these states aboveT_HO, combined with a more detailed theoretical investigation of this region, suggests a key role of theN-point in the hidden order transition.

    

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4. A Luminous Red Supergiant and Dusty Long-period Variable Progenitor for SN 2023ixf

   https://doi.org/10.3847/2041-8213/ace618  

   Jencson, Jacob E. ; Pearson, Jeniveve ; Beasor, Emma R. ; Lau, Ryan M. ; Andrews, Jennifer E. ; Bostroem, K. Azalee ; Dong 董, Yize 一泽 ; Engesser, Michael ; Gomez, Sebastian ; Guolo, Muryel ; et al ( July 2023 , The Astrophysical Journal Letters)

   We analyze pre-explosion near- and mid-infrared (IR) imaging of the site of SN 2023ixf in the nearby spiral galaxy M101 and characterize the candidate progenitor star. The star displays compelling evidence of variability with a possible period of ≈1000 days and an amplitude of Δm≈ 0.6 mag in extensive monitoring with the Spitzer Space Telescope since 2004, likely indicative of radial pulsations. Variability consistent with this period is also seen in the near-IRJandK_sbands between 2010 and 2023, up to just 10 days before the explosion. Beyond the periodic variability, we do not find evidence for any IR-bright pre-supernova outbursts in this time period. The IR brightness ($M_{K_s}=-10.7$mag) and color (J−K_s= 1.6 mag) of the star suggest a luminous and dusty red supergiant. Modeling of the phase-averaged spectral energy distribution (SED) yields constraints on the stellar temperature ($T_{\mathrm{eff}}={3500}_{-1400}^{+800}$K) and luminosity ($\log L/L_{\odot }=5.1\pm 0.2$). This places the candidate among the most luminous Type II supernova progenitors with direct imaging constraints, with the caveat that many of these rely only on optical measurements. Comparison with stellar evolution models gives an initial mass ofM_init= 17 ± 4M_⊙. We estimate the pre-supernova mass-loss rate of the star between 3 and 19 yr before explosion from the SED modeling at$\dot{M}\approx 3\times {10}^{-5}$to 3 × 10⁻⁴M_⊙yr⁻¹for an assumed wind velocity ofv_w= 10 km s⁻¹, perhaps pointing to enhanced mass loss in a pulsation-driven wind.

    

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5. Interface Thermal Resistance between Monolayer WSe 2 and SiO 2 : Raman Probing with Consideration of Optical–Acoustic Phonon Nonequilibrium

   https://doi.org/10.1002/admi.202102059  

   Hunter, Nicholas ; Azam, Nurul ; Zobeiri, Hamidreza ; Van Velson, Nathan ; Mahjouri‐Samani, Masoud ; Wang, Xinwei ( January 2022 , Advanced Materials Interfaces)

   This work explores the 2D interfacial energy transport between monolayer WSe₂and SiO₂while considering the thermal nonequilibrium between optical and acoustic phonons caused by photoexcitation. Recent modeling and experimental work have shown substantial temperature differences between optical and acoustic phonons (ΔT_OA) in various nanostructures upon laser irradiation. Generally, characterizations of interfacial thermal resistance (R′′_tc) at the nanoscale are difficult and depend on Raman‐probed temperature measurements, which only reveal optical phonon temperature information. Here it is shown that ΔT_OAfor supported monolayer WSe₂can be as high as 48% of the total temperature rise revealed by optothermal Raman methods—a significant proportion that can introduce sizeable error toR′′_tcmeasurements if not properly considered. A frequency energy transport state‐resolved Raman technique (FET‐Raman) along with a 3D finite volume modeling of 2D material laser heating is used to extract the true interfacial thermal resistanceR′′_tc(determined by acoustic phonon transport). Additionally, a novel ET‐Raman technique is developed to determine the energy coupling factorGbetween optical and acoustic phonons (on the order of 10¹⁵W m⁻³K⁻¹). This work demonstrates the need for special consideration of thermal nonequilibriums during laser–matter interactions at the nanoscale.

    

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