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1. Structure and equation of state of Bi2Sr2Can−1CunO2n+4+δ from x-ray diffraction to megabar pressures

   https://doi.org/10.1103/PhysRevMaterials.7.064803  

   Mark, Alexander C. ; Ahart, Muhtar ; Kumar, Ravhi ; Park, Changyong ; Meng, Yue ; Popov, Dmitry ; Deng, Liangzi ; Chu, Ching-Wu ; Campuzano, Juan Carlos ; Hemley, Russell J. ( June 2023 , Physical Review Materials)

   - (Ed.)

   Pressure is a unique tuning parameter for probing the properties of materials, and it has been particularly useful for studies of electronic materials such as high-temperature cuprate superconductors. Here we report the effects of quasihydrostatic compression produced by a neon pressure medium on the structures of bismuth-based high-Tc cuprate superconductors with the nominal composition Bi2Sr2Can−1CunO2n+4+δ (n = 1, 2, 3) up to 155 GPa. The structures of all three compositions obtained by synchrotron x-ray diffraction can be described as pseudotetragonal over the entire pressure range studied. We show that previously reported pressure-induced distortions and structural changes arise from the large strains that can be induced in these layered materials by nonhydrostatic stresses. The pressure-volume equations of state (EOS) measured under these quasihydrostatic conditions cannot be fit to single phenomenological formulation over the pressure ranges studied, starting below 20 GPa. This intrinsic anomalous compression as well as the sensitivity of Bi2Sr2Can−1CunO2n+4+δ to deviatoric stresses provide explanations for the numerous inconsistencies in reported EOS parameters for these materials. We conclude that the anomalous compressional behavior of all three compositions is a manifestation of the changes in electronic properties that are also responsible for the remarkable nonmonotonic dependence of Tc with pressure, including the increase in Tc at the highest pressures studied so far for each. Transport and spectroscopic measurements up to megabar pressures are needed to fully characterize these cuprates and explore higher possible critical temperatures in these materials. 

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2. Robust superconductivity and the suppression of charge-density wave in the quasi-skutterudites Ca3(Ir1−xRhx)4Sn13 single crystals at ambient pressure

   https://doi.org/10.1088/1361-648X/ad5485  

   Krenkel, Elizabeth_H ; Tanatar, Makariy_A ; Ghimire, Sunil ; Joshi, Kamal_R ; Chen, Shuzhang ; Petrovic, Cedomir ; Prozorov, Ruslan ( June 2024 , Journal of Physics: Condensed Matter)

   Single crystals of the quasi-skutterudite compounds Ca₃(Ir_1-xRh_x)₄Sn₁₃(3–4–13) were synthesized by flux growth and characterized by x-ray diffraction, energy dispersive x-ray spectroscopy, magnetization, resistivity, and radio frequency magnetic susceptibility techniques. The coexistence and competition between the charge density wave (CDW) and superconductivity was studied by varying the Rh/Ir ratio. The superconducting transition temperature,$T_{\mathrm{c}}$, varies from 7 K in pure Ir (x = 0) to 8.3 K in pure Rh (x = 1). Temperature-dependent electrical resistivity reveals monotonic suppression of the CDW transition temperature,T_CDW(x). The CDW starts in pure Ir,x = 0, atT_CDW≈ 40 K and extrapolates roughly linearly to zero at$x_c\approx$0.53–0.58 under the superconducting dome. Magnetization and transport measurements show a significant influence of CDW on superconducting and normal states. Meissner expulsion is substantially reduced in the CDW region, indicating competition between the CDW and superconductivity. The low-temperature resistivity is higher in the CDW part of the phase diagram, consistent with the reduced density of states due to CDW gapping. Its temperature dependence just above$T_{\mathrm{c}}$shows signs of non-Fermi liquid behavior in a cone-like composition pattern. We conclude that the Ca₃(Ir_1-xRh_x)₄Sn₁₃alloy is a good candidate for a composition-driven quantum critical point at ambient pressure.

    

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3. Measurement of the Static Stark Shift of the 7s S21/2 Level in Atomic Cesium

   https://doi.org/10.1103/PhysRevLett.132.233201  

   Quirk, Jonah A ; Jacobsen, Aidan ; Damitz, Amy ; Tanner, Carol E ; Elliott, D S ( June 2024 , Physical Review Letters)

   We report a new precision measurement of the dc Stark shift of the $6s\hspace{1mm} ^2S_{1/2} \rightarrow 7s\hspace{1mm}^2S_{1/2}$ transition in atomic cesium-133. Our result is 0.72246 (29) $\textrm{Hz}(\textrm{V}/\textrm{cm})^{-2}$. This result differs from a previous measurement of the Stark shift by $\sim$0.5\%, or 4.7$\sigma$. We use this value to recalculate the magnitude of the reduced dipole matrix elements $\langle7s ||r||7p_{j}\rangle$, as well as the vector transition polarizability for the $6s \rightarrow 7s$ transition, $\tilde{\beta} = 27.043 \: (36) \ a_0^3$. This determination helps resolve a critical discrepancy between two techniques for determining the vector polarizability. 

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4. Search for long-lived heavy neutral leptons decaying in the CMS muon detectors in proton-proton collisions at s=13  TeV

   https://doi.org/10.1103/PhysRevD.110.012004  

   Hayrapetyan, A ; Tumasyan, A ; Adam, W ; Andrejkovic, J W ; Bergauer, T ; Chatterjee, S ; Damanakis, K ; Dragicevic, M ; Hussain, P S ; Jeitler, M ; et al ( July 2024 , Physical Review D)

   A search for heavy neutral leptons (HNLs) decaying in the CMS muon system is presented. A data sample is used corresponding to an integrated luminosity of$138{\mathrm{fb}}^{-1}$of proton-proton collisions at$\sqrt{s}=13\mathrm{TeV}$, recorded at the CERN LHC in 2016–2018. Decay products of long-lived HNLs could interact with the shielding materials in the CMS muon system and create hadronic and electromagnetic showers detected in the muon chambers. This distinctive signature provides a unique handle to search for HNLs with masses below 4 GeV and proper decay lengths of the order of meters. The signature is sensitive to HNL couplings to all three generations of leptons. Candidate events are required to contain a prompt electron or muon originating from a vertex on the beam axis and a displaced shower in the muon chambers. No significant deviations from the standard model background expectation are observed. In the electron (muon) channel, the most stringent limits to date are set for HNLs in the mass range of 2.1–3.0 (1.9–3.3) GeV, reaching mixing matrix element squared values as low as$8.6(4.6)\times {10}^{-6}$.

   © 2024 CERN, for the CMS Collaboration2024CERN 

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5. Search for a scalar or pseudoscalar dilepton resonance produced in association with a massive vector boson or top quark-antiquark pair in multilepton events at s=13  TeV

   https://doi.org/10.1103/PhysRevD.110.012013  

   Tumasyan, A ; Adam, W ; Andrejkovic, J W ; Bergauer, T ; Chatterjee, S ; Damanakis, K ; Dragicevic, M ; Escalante_Del_Valle, A ; Hussain, P S ; Jeitler, M ; et al ( July 2024 , Physical Review D)

   A search for beyond the standard model spin-0 bosons,$\varphi$, that decay into pairs of electrons, muons, or tau leptons is presented. The search targets the associated production of such bosons with a$W$or$Z$gauge boson, or a top quark-antiquark pair, and uses events with three or four charged leptons, including hadronically decaying tau leptons. The proton-proton collision data set used in the analysis was collected at the LHC from 2016 to 2018 at a center-of-mass energy of 13 TeV, and corresponds to an integrated luminosity of$138{\mathrm{fb}}^{-1}$. The observations are consistent with the predictions from standard model processes. Upper limits are placed on the product of cross sections and branching fractions of such new particles over the mass range of 15 to 350 GeV with scalar, pseudoscalar, or Higgs-boson-like couplings, as well as on the product of coupling parameters and branching fractions. Several model-dependent exclusion limits are also presented. For a Higgs-boson-like$\varphi$model, limits are set on the mixing angle of the Higgs boson with the$\varphi$boson. For the associated production of a$\varphi$boson with a top quark-antiquark pair, limits are set on the coupling to top quarks. Finally, limits are set for the first time on a fermiophilic dilaton-like model with scalar couplings and a fermiophilic axion-like model with pseudoscalar couplings.