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1. Study the structure of the low-lying states of 206 Po

   https://doi.org/10.1088/1402-4896/ad4521  

   Kocheva, D ; Rainovski, G ; Jolie, J ; Beckers, M ; Blazhev, A ; Esmaylzadeh, A ; Fransen, C ; Gladnishki, K A ; Pietralla, N ; Scheck, M ; et al ( May 2024 , Physica Scripta)

   The nucleus²⁰⁶Po was studied in the two proton transfer reaction²⁰⁴Pb(¹⁶O,¹⁴C)²⁰⁶Po and the lifetime of the first excited 2⁺state was determined by utilizing the Recoil Distance Doppler Shift method. The experimental results are compared with shell-model calculations based on different effective interactions. The calculations qualitatively reproduced the experimentally observed$B(E2;2_1^{+}\to 0_1^{+})$value, suggesting that the$2_1^{+}$state of²⁰⁶Po exhibits a collective nature. However, the employed effective interactions revealed some limitations, particularly in their description of the$4_{1,2}^{+}$states. These results emphasize the importance of understanding the properties of low-lying states, especially their evolution from single-particle dynamics to collective modes, in evaluating various effective nuclear interactions.

    

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2. Electron Heating in 2D Particle-in-cell Simulations of Quasi-perpendicular Low-beta Shocks

   https://doi.org/10.3847/1538-4357/ad1f69  

   Tran, Aaron ; Sironi, Lorenzo ( April 2024 , The Astrophysical Journal)

   We measure the thermal electron energization in 1D and 2D particle-in-cell simulations of quasi-perpendicular, low-beta (β_p= 0.25) collisionless ion–electron shocks with mass ratiom_i/m_e= 200, fast Mach number${\mathcal{M}}_{\mathrm{ms}}=1$–4, and upstream magnetic field angleθ_Bn= 55°–85° from the shock normal$\hat{\mathit{n}}$. It is known that shock electron heating is described by an ambipolar,B-parallel electric potential jump, Δϕ_∥, that scales roughly linearly with the electron temperature jump. Our simulations have$\mathrm{\Delta }{\varphi }_{\parallel }/(0.5m_{\mathrm{i}}{u_{\mathrm{sh}}}^2)\sim 0.1$–0.2 in units of the pre-shock ions’ bulk kinetic energy, in agreement with prior measurements and simulations. Different ways to measureϕ_∥, including the use of de Hoffmann–Teller frame fields, agree to tens-of-percent accuracy. Neglecting off-diagonal electron pressure tensor terms can lead to a systematic underestimate ofϕ_∥in our low-β_pshocks. We further focus on twoθ_Bn= 65° shocks: a${\mathcal{M}}_{\mathrm{s}}=4$(${\mathcal{M}}_{\mathrm{A}}=1.8$) case with a long, 30d_iprecursor of whistler waves along$\hat{\mathit{n}}$, and a${\mathcal{M}}_{\mathrm{s}}=7$(${\mathcal{M}}_{\mathrm{A}}=3.2$) case with a shorter, 5d_iprecursor of whistlers oblique to both$\hat{\mathit{n}}$andB;d_iis the ion skin depth. Within the precursors,ϕ_∥has a secular rise toward the shock along multiple whistler wavelengths and also has localized spikes within magnetic troughs. In a 1D simulation of the${\mathcal{M}}_{\mathrm{s}}=4$,θ_Bn= 65° case,ϕ_∥shows a weak dependence on the electron plasma-to-cyclotron frequency ratioω_pe/Ω_ce, andϕ_∥decreases by a factor of 2 asm_i/m_eis raised to the true proton–electron value of 1836.

    

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3. Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged inside the Debris Disk of the Young Star AF Lep

   https://doi.org/10.3847/2041-8213/acd6f6  

   Franson, Kyle ; Bowler, Brendan P. ; Zhou, Yifan ; Pearce, Tim D. ; Bardalez Gagliuffi, Daniella C. ; Biddle, Lauren I. ; Brandt, Timothy D. ; Crepp, Justin R. ; Dupuy, Trent J. ; Faherty, Jacqueline ; et al ( June 2023 , The Astrophysical Journal Letters)

   We present the direct-imaging discovery of a giant planet orbiting the young star AF Lep, a 1.2M_⊙member of the 24 ± 3 MyrβPic moving group. AF Lep was observed as part of our ongoing high-contrast imaging program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions. Keck/NIRC2 observations in$L\prime$with the vector vortex coronagraph reveal a point source, AF Lep b, at ≈340 mas, which exhibits orbital motion at the 6σlevel over the course of 13 months. A joint orbit fit yields precise constraints on the planet’s dynamical mass of${3.2}_{-0.6}^{+0.7}$M_Jup, semimajor axis of${8.4}_{-1.3}^{+1.1}$au, and eccentricity of${0.24}_{-0.15}^{+0.27}$. AF Lep hosts a debris disk located at ∼50 au, but it is unlikely to be sculpted by AF Lep b, implying there may be additional planets in the system at wider separations. The stellar inclination (i_*=${54}_{-9}^{+11}°$) and orbital inclination (i_o=${50}_{-12}^{+9}°$) are in good agreement, which is consistent with the system having spin–orbit alignment. AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement and highlights the promise of using astrometric accelerations as a tool to find and characterize long-period planets.

    

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4. Tuning metal/superconductor to insulator/superconductor coupling via control of proximity enhancement between NbSe 2 monolayers

   https://doi.org/10.1088/1361-648X/acbf92  

   Chiatti, Olivio ; Mihov, Klara ; Griffin, Theodor U. ; Grosse, Corinna ; Alemayehu, Matti B. ; Hite, Kyle ; Hamann, Danielle ; Mogilatenko, Anna ; Johnson, David C. ; Fischer, Saskia F. ( March 2023 , Journal of Physics: Condensed Matter)

   The interplay between charge transfer and electronic disorder in transition-metal dichalcogenide multilayers gives rise to superconductive coupling driven by proximity enhancement, tunneling and superconducting fluctuations, of a yet unwieldy variety. Artificial spacer layers introduced with atomic precision change the density of states by charge transfer. Here, we tune the superconductive coupling between$\text{NbS}{\text{e}}_{\text{2}}$monolayers from proximity-enhanced to tunneling-dominated. We correlate normal and superconducting properties in${\left[{\left(\text{SnSe}\right)}_{1+\delta }\right]}_m{\left[\text{NbS}{\text{e}}_{\text{2}}\right]}_1$tailored multilayers with varying SnSe layer thickness ($m=1-15$). From high-field magnetotransport the critical fields yield Ginzburg–Landau coherence lengths with an increase of$140\mathrm{\%}$cross-plane ($m=1-9$), trending towards two-dimensional superconductivity for$m>9$. We show cross-overs between three regimes: metallic with proximity-enhanced coupling ($m=1-4$), disordered-metallic with intermediate coupling ($m=5-9$) and insulating with Josephson tunneling ($m>9$). Our results demonstrate that stacking metal mono- and dichalcogenides allows to convert a metal/superconductor into an insulator/superconductor system, prospecting the control of two-dimensional superconductivity in embedded layers.

    

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5. Characterizing the fundamental bending vibration of a linear polyatomic molecule for symmetry violation searches

   https://doi.org/10.1088/1367-2630/ace471  

   Jadbabaie, Arian ; Takahashi, Yuiki ; Pilgram, Nickolas H ; Conn, Chandler J ; Zeng, Yi ; Zhang, Chi ; Hutzler, Nicholas R ( July 2023 , New Journal of Physics)

   Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of${}^{174}$YbOH using high-resolution optical spectroscopy on the nominally forbidden$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$$\to \tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(000)$transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state and fit the molecule-frame dipole moment to$D_{\mathrm{m}\mathrm{o}\mathrm{l}}=2.16(1)$Dand the effective electrong-factor to$g_S=2.07(2)$. Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin–orbit and vibronic perturbations in the excited$\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(000)$state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.

    

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