The transition-metal-based kagome metals provide a versatile platform for correlated topological phases hosting various electronic instabilities. While superconductivity is rare in layered kagome ...compounds, its interplay with nontrivial topology could offer an engaging space to realize exotic excitations of quasiparticles. Here, we use scanning tunneling microscopy to study a newly discoveredZ2topological kagome metalCsV3Sb5with a superconducting ground state. We observe charge modulation associated with the opening of an energy gap near the Fermi level. When across single-unit-cell surface step edges, the intensity of this charge modulation exhibits aπ-phase shift, suggesting a three-dimensional2×2×2charge density wave ordering. Interestingly, while conventional Caroli–de Gennes–Matricon bound states are observed inside the superconducting vortex on the Sb surfaces, a robust zero-bias conductance peak emerges that does not split in a large distance when moving away from the vortex center on the Cs2×2surfaces, resembling the Majorana bound states arising from the superconducting Dirac surface states inBi2Te3/NbSe2heterostructures. Our findings establishCsV3Sb5as a promising candidate for realizing exotic excitations at the confluence of nontrivial lattice geometry, topology and multiple electronic orders.
Since the discovery of high-transition-temperature (high-T(c)) superconductivity in layered copper oxides, extensive effort has been devoted to exploring the origins of this phenomenon. A T(c) higher ...than 40 K (about the theoretical maximum predicted from Bardeen-Cooper-Schrieffer theory), however, has been obtained only in the copper oxide superconductors. The highest reported value for non-copper-oxide bulk superconductivity is T(c) = 39 K in MgB(2) (ref. 2). The layered rare-earth metal oxypnictides LnOFeAs (where Ln is La-Nd, Sm and Gd) are now attracting attention following the discovery of superconductivity at 26 K in the iron-based LaO(1-x)F(x)FeAs (ref. 3). Here we report the discovery of bulk superconductivity in the related compound SmFeAsO(1-x)F(x), which has a ZrCuSiAs-type structure. Resistivity and magnetization measurements reveal a transition temperature as high as 43 K. This provides a new material base for studying the origin of high-temperature superconductivity.
We have elucidated here the interplay between reversed austenite and plastic deformation in a directly quenched and intercritically annealed medium-manganese low-Al steel in terms of microstructural ...evolution and mechanical properties. The ultra-low carbon 5Mn steel was subjected to controlled rolling and direct quenching, followed by intercritical annealing at 630 °C and 650 °C for 30 min, respectively. The directly quenched steel consisted of thin lath-martensite of ∼0.2–0.9 μm thickness and ∼1.7–2.0% retained austenite with ∼50 nm thickness. Intercritical annealing led to a microstructure consisting of alternate sub-micron laminated structure of tempered martensite and reversed austenite. With increase in annealing temperature from 630 °C to 650 °C, the volume fraction of austenite was increased from 12.6% to 19.1% at 1/4 thickness (t/4), and from 8.4% to 12.7% at 1/2 thickness (t/2). The yield strength, tensile strength, and elongation of 728 MPa, 826 MPa, and 25.5%, were obtained at t/4 of the plate, and 714 MPa, 814 MPa, and 24.2% at t/2, on annealing at 630 °C. The impact energy obtained at −60 °C was greater than 80 J. When the annealing temperature was increased to 650 °C, strength was marginally decreased, but toughness was significantly increased to more than 110 J. Extremely small variation in microstructure and mechanical properties at t/4 and t/2 plate thickness were observed. Energy dispersive x-ray spectroscopy (EDS) confirmed ∼7.2–10.1 wt% Mn enrichment in reversed austenite during annealing, which is of significance in stabilization of reversed austenite. Work hardening behavior and tensile experiments were conducted to study the effect of reversed austenite during plastic deformation. With increased annealing temperature, the stability of reversed austenite was decreased because of less enrichment of C and Mn in reversed austenite and grain growth. At 0.05 tensile strain, reversed austenite transformed to twin-type martensite, implying occurrence of transformation induced plasticity (TRIP) effect.
•The homogeneity of heavy plate steel was improved by innovative use of 5Mn alloying.•Short processing of direct quenching and intercritical annealing was adopted.•Sub-micron laminated structure of tempered martensite-austenite enhanced strength.•Mn partitioning from martensite to austenite improved the stability of austenite.•The TRIP effect of reversed austenite significantly enhanced ductility and toughness.
We report constraints on the dark photon effective kinetic mixing parameter (κ) with data taken from two p-type point-contact germanium detectors of the CDEX-10 experiment at the China Jinping ...Underground Laboratory. The 90% confidence level upper limits on κ of solar dark photon from 205.4 kg-day exposure are derived, probing new parameter space with masses (m_{V}) from 10 to 300 eV/c^{2} in direct detection experiments. Considering dark photon as the cosmological dark matter, limits at 90% confidence level with m_{V} from 0.1 to 4.0 keV/c^{2} are set from 449.6 kg-day data, with a minimum of κ=1.3×10^{-15} at m_{V}=200 eV/c^{2}.
The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for ...energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.
A search for exotic dark matter (DM) in the sub-GeV mass range has been conducted using 205 kg day data taken from a p-type point contact germanium detector of the CDEX-10 experiment at China's ...Jinping underground laboratory. New low-mass dark matter searching channels, neutral current fermionic DM absorption (χ+A→ν+A) and DM-nucleus 3→2 scattering (χ+χ+A→ϕ+A), have been analyzed with an energy threshold of 160 eVee. No significant signal was found; thus new limits on the DM-nucleon interaction cross section are set for both models at the sub-GeV DM mass region. A cross section limit for the fermionic DM absorption is set to be 2.5×10^{-46} cm^{2} (90% C.L.) at DM mass of 10 MeV/c^{2}. For the DM-nucleus 3→2 scattering scenario, limits are extended to DM mass of 5 and 14 MeV/c^{2} for the massless dark photon and bound DM final state, respectively.
The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This ...work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2
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years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.
The focal plane camera is the core component of the Wide Field-of-view Cherenkov/fluorescence Telescope Array (WFCTA) of the Large High-Altitude Air Shower Observatory (LHAASO). Because of the ...capability of working under moonlight without aging, silicon photomultipliers (SiPM) have been proven to be not only an alternative but also an improvement to conventional photomultiplier tubes (PMT) in this application. Eighteen SiPM-based cameras with square light funnels have been built for WFCTA. The telescopes have collected more than 100 million cosmic ray events and preliminary results indicate that these cameras are capable of working under moonlight. The characteristics of the light funnels and SiPMs pose challenges (e.g. dynamic range, dark count rate, assembly techniques). In this paper, we present the design features, manufacturing techniques and performances of these cameras. Finally, the test facilities, the test methods and results of SiPMs in the cameras are reported here.
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