Electron-impact Ionization of Atomic Nitrogen

New electron-impact ionization (EII) data are presented for neutral atomic nitrogen. The atom is treated as a 67-state system, incorporating Rydberg values up to n=20. State-specific cross sections for the first three states are from published B-spline R-matrix-with-pseudostates results. Binary-encounter Bethe calculations have been performed for the remaining 64 states. These data are designed for modeling the hypersonic chemistry that occurs when a space vehicle enters Earth’s atmosphere from beyond orbit. The cross sections have been convolved into state-specific thermal rate coefficients and fit with the commonly used Arrhenius–Kooij formula for ease of use in shock-heated air plasma models. Additionally, rate coefficients are provided for a reduced 10-state system for use in coarse-grain models. For a given collisional–radiative model, these fine- and coarse-grain data can be used to generate state-specific rate coefficients for three-body electron–ion recombination, the time-reverse process of EII

Reply to "Comment on 'Nontrivial Quantum Geometry and the Strength of Electron-Phonon Coupling', arXiv:2305.02340, J. Yu, C. J. Ciccarino, R. Bianco, I. Errea, P. Narang, B. A. Bernevig"

This is our reply to "Comment on 'Nontrivial Quantum Geometry and the Strength of Electron-Phonon Coupling', arXiv:2305.02340, J. Yu, C. J. Ciccarino, R. Bianco, I. Errea, P. Narang, B. A. Bernevig" by Prof. Pickett, which focuses on the MgB$_2$ part of our work. We show that the entirety of the criticism in Prof. Pickett's comment pertaining to our work (arXiv:2305.02340) is invalid.Comment: 3+3 pages, 1 figur

Lead-related quantum emitters in diamond

We report on quantum emission from Pb-related color centers in diamond following ion implantation and high-temperature vacuum annealing. First-principles calculations predict a negatively charged Pb-vacancy (PbV) center in a split-vacancy configuration, with a zero-phonon transition around 2.4 eV. Cryogenic photoluminescence measurements performed on emitters in nanofabricated pillars reveal several transitions, including a prominent doublet near 520 nm. The splitting of this doublet, 5.7 THz, exceeds that reported for other group-IV centers. These observations are consistent with the PbV center, which is expected to have a combination of narrow optical transitions and stable spin states, making it a promising system for quantum network nodes.U.S. Army Research Laboratory. Center for Distributed Quantum InformationNational Science Foundation (U.S.). Graduate Research Fellowship ProgramNational Science Foundation (U.S.) (Grant DMR-1231319)United States. National Aeronautics and Space Administration (Space Technology Research Fellowship)MIT-Harvard Center for Ultracold Atoms MIT International Science and Technology Initiativ

Phonon Polaritons in Monolayers of Hexagonal Boron Nitride.

Phonon polaritons in van der Waals materials reveal significant confinement accompanied with long propagation length: important virtues for tasks pertaining to the control of light and energy flow at the nanoscale. While previous studies of phonon polaritons have relied on relatively thick samples, here reported is the first observation of surface phonon polaritons in single atomic layers and bilayers of hexagonal boron nitride (hBN). Using antenna-based near-field microscopy, propagating surface phonon polaritons in mono- and bilayer hBN microcrystals are imaged. Phonon polaritons in monolayer hBN are confined in a volume about one million times smaller than the free-space photons. Both the polariton dispersion and their wavelength-thickness scaling law are altered compared to those of hBN bulk counterparts. These changes are attributed to phonon hardening in monolayer-thick crystals. The data reported here have bearing on applications of polaritons in metasurfaces and ultrathin optical elements