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Physics and Engineering Physics

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    A new highly stable multifunctional two-dimensional Si2BN monolayer quantum material with a direct bandgap predicted by density functional theory
    (Royal Society of Chemistry [Society Publisher], 2024-07) Djamel, Bezzerga; Chelil, Naouel; Mohammed, Sahnoun; Gusarov, Sergey; Chang, Gap Soo; Naseri, Mosayeb
    In this work, we present a novel two-dimensional (2D) Si2BN structure (2D ή-Si2BN) predicted using density functional theory (DFT). The proposed structure exhibits a unique double quasi-planar layer interconnected by covalent bonds, demonstrating lower energy compared to the previously reported planar Si2BN nanosheet. Our calculations, conducted at the HSE06 level of theory, reveal its semiconductor nature with a direct band gap of 1.24 eV at the gamma point. The 2D material exhibits exceptional light absorption in the visible region, prompting an exploration of its potential in photovoltaic applications. Remarkably, our findings indicate a maximum theoretical efficiency of 27.6%, underscoring its promise for renewable energy technologies. Furthermore, employing modern polarization theory, we unveil the ferroelectric properties of the Si2BN monolayer. Notably, a large out-of-plane polarization is observed. It was found that the unstrained 2D ή-Si2BN monolayer demonstrates an impressive out-of-plane spontaneous electric polarization of 28.98 × 10−10 C m−1, a value six times greater than previously referenced Janus materials. This remarkable enhancement in ferroelectric capabilities positions the Si2BN monolayer as a promising candidate for applications in next generation novel information storage, nano-electronic, and optoelectronic devices. These findings not only contribute to the understanding of the structural and electronic properties of the 2D ή-Si2BN monolayer but also highlight its potential for various technological applications, marking a significant advancement in the field of nanomaterials.
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    Bounds on 𝑎_𝜇^(HVP,LO) using Hölder's inequalities and finite-energy QCD sum rules
    (Elsevier, 2024-09-26) Li, Siyuan; Steele, Tom; Ho, Jason; R-Rahaman, Raza; Williams, K.; Kleiv, Robin
    This study establishes bounds on the leading-order (LO) hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon (𝑎_𝜇^(HVP,LO), 𝑎𝜇 = (𝑔 − 2)𝜇∕2) by using Hölder’s inequality and related inequalities in Finite-Energy QCD sum rules. Considering contributions from light quarks (𝑱, 𝑑, 𝑠) up to five-loop order in perturbation theory within the chiral limit, leading-order light-quark mass corrections, next-to-leading order for dimension-four QCD condensates, and leading-order for dimension-six QCD condensates, the study finds QCD lower and upper bounds as (657.0 ± 34.8) × 10−10 ≀ 𝑎_𝜇^(HVP,LO) ≀ (788.4 ± 41.8) × 10−10.
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    Negative Charge Transfer Energy in Correlated Compounds
    (Physical Society of Japan, 2024-09-13) Green, Robert J.; Sawatzky, George A.
    In correlated compounds containing cations in high formal oxidation states (assigned by assuming that anions attain full valence shells), the energy of ligand to cation charge transfer can become small or even negative. This yields compounds with a high degree of covalence and can lead to a self-doping of holes into the ligand states of the valence band. Such compounds are of particular topical interest, as highly studied perovskite oxides containing trivalent nickel or tetravalent iron are negative charge transfer systems, as are nickel-containing lithium ion battery cathode materials. In this report, we review the topic of negative charge transfer energy, with an emphasis on plots and diagrams as analysis tools, in the spirit of the celebrated Tanabe–Sugano diagrams which are the focus of this Special Topics Issue.
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    P1−xTa8+xN13 (x=0.1–0.15): A Phosphorus Tantalum Nitride Featuring Mixed-Valent Tantalum and P/Ta Disorder Visualized by Scanning Transmission Electron Microscopy
    (Angewandte Chemie International Edition, 2024-07) Pointner, Monika Martina; Ceniza, Claude; Nusser, Lukas; Witthaut, Kristian; Wolf, Florian; Weidemann, Martin; Eisenburger, Lucien; Moewes, Alexander; Oeckler, Oliver; Schnick, Wolfgang
    We report on the synthesis, crystal, and electronic structure, as well as the magnetic, and electric properties of the phosphorus-containing tantalum nitride P1−xTa8+xN13 (x=0.1–0.15). A high-pressure high-temperature reaction (8 GPa, 1400 °C) of Ta3N5 and P3N5 with NH4F as a mineralizing agent yields the compound in the form of black, rod-shaped crystals. Single-crystal X-ray structure elucidation (space group C2/m (no. 12), a=16.202(3), b=2.9155(4), c=11.089(2) Å, ÎČ=126.698(7)°, Z=2) shows a network of face- and edge-sharing Ta-centered polyhedra that contains small vacant channels and PN6 octahedra strands. Atomic resolution transmission electron microscopy reveals an unusual P/Ta disorder. Mixed-valent tantalum atoms exhibit interatomic distances similar to those in metallic tantalum, however, the electrical resistivity is quite high in the order of 101 Ω cm. The density of states and the electron localization function indicate localized electrons in both covalent and ionic bonds between P/Ta and N atoms, combined with less localized electrons that do not contribute to interatomic bonds.
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    Unraveling the electronic structure and magnetic transition evolution across monolayer, bilayer, and multilayer ferromagnetic Fe3GeTe2
    (npj 2D Materials and Applications volume, 2024-09-30) Roemer, Ryan; Lee, Dong Hyun David; Smit, Steef; Zhang, Xiyue; Godin, Simon; Hamza, V; Jian, Tianyi; Larkin, Josiah; Shin, H; Liu, Chong; Michiardi, Matteo; Levy, Giorgio; Zhang, Zhan; Green, Robert; Kim, C; Muller, David; damascelli, andrea; Han, Myung Joon; Zou, Ke
    Two-dimensional (2D) van der Waals (vdW) magnets have sparked widespread attention due to their potential in spintronic applications as well as in fundamental physics. Ferromagnetic vdW compound Fe3GeTe2 (FGT) and its Ga variants have garnered significant interest due to their itinerant magnetism, correlated states, and high magnetic transition temperature. Experimental studies have demonstrated the tunability of FGT’s Curie temperature, TC, through adjustments in quintuple layer numbers (QL) and carrier concentrations, n. However, the underlying mechanism remains elusive. In this study, we employ molecular beam epitaxy (MBE) to synthesize 2D FGT films down to 1 QL with precise layer control, facilitating an exploration of the band structure and the evolution of itinerant carrier density. Angle-resolved photoemission spectroscopy (ARPES) reveals significant band structure changes at the ultra-thin limit, while first-principles calculations elucidate the band evolution from 1 QL to bulk, largely governed by interlayer coupling. Additionally, we find that n is intrinsically linked to the number of QL and temperature, with a critical value triggering the magnetic phase transition. Our findings underscore the pivotal role of band structure and itinerant electrons in governing magnetic phase transitions in such 2D vdW magnetic materials.