Sr2Cr3As2O2 is composed of alternating square-lattice CrO2 and Cr2As2 stacking layers, where CrO2 is isostructural to the CuO2 building-block of cuprate high-Tc superconductors and Cr2As2 to Fe2As2 of Fe-based superconductors. Current interest in this material is raised by theoretic prediction of possible superconductivity. In this neutron powder diffraction study, we discovered that magnetic moments of Cr(II) ions in the Cr2As2 sublattice develop a C-type antiferromagnetic structure below 590 K, and the moments of Cr(I) in the CrO2 sublattice form the La2CuO4-like antiferromagnetic order below 291 K. The staggered magnetic moment 2.19(4)µB /Cr(II) in the more itinerant Cr2As2 layer is smaller than 3.10(6)µB /Cr(I) in the more localized CrO2 layer. Different from previous expectation, a spin-flop transition of the Cr(II) magnetic order observed at 291 K indicates a strong coupling between the CrO2 and Cr2As2 magnetic subsystems.

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Soot, also known as black carbon (BC), is a typical aerosol particle. It plays the major role of light-absorbing carbonaceous component of fine particles and forms during the incomplete combustion of biomass and fossil fuels (Bond et al., 2013). Soot particle has been considered as the second largest anthropogenic radiative forcer in the present-day climate after CO 2 (Boucher et al., 2013). It plays a significant role in global warming by affecting the radiative balance at both global and regional scales (

We report the results of electrical resistivity, magnetic and thermodynamic measurements on polycrystalline SnSb, whose structure consists of stacks of Sb bilayers and Sn 4 Sb 3 septuple layers along the c-axis. The material is found to be a weakly coupled, fully gapped, type-II superconductor with a bulk T c of 1.50 K, while showing a zero resistivity transition at a significantly higher temperature of 2.48 K. The Sommerfeld coefficient and upper critical field, obtained from specific heat measurements, are 2.29 mJ mol −1 K −2 and 520 Oe, respectively. Compositional inhomogeneity and strain effect at the grain boundaries are proposed as possible origins for the difference in resistive and bulk superconducting transitions. In addition, a comparison with the rock-salt structure SnAs superconductor is presented. Our results provide the first clear evidence of bulk superconductivity in a natural superlattice derived from a topological semimetal.

We report the discovery of superconductivity in binary alloy Sn1−xSbx with x in the range of 0.43 to 0.6, which possesses a modulated rhombohedral structure due to the incommensurate ordering of Sn and Sb layers along the c-axis. The specific heat measurements indicate a weakly coupled, fully gapped superconducting state in this homogeneity range with a maximum bulk Tc of 1.58 K at x = 0.46, though the electronic specific heat and Hall coefficients remain nearly x-independent. The nonmonotonic dependence of the bulk Tc is discussed in relation to the effects of Sb-layer intercalation between the [Sn4Sb3] seven-layer lamellae that are the essential building block for superconductivity. On the other hand, a zero-resistivity transition is found to take place well above the bulk superconducting transition, and the corresponding Tc increases monotonically with x from 2.06 K to 3.29 K. This contrast, together with the uniform elements distribution revealed by energy dispersive x-ray mapping, implies that the resistive transition is due to the strain effect at the grain boundary rather than the compositional inhomogeneity. The first-principles calculations on the representative composition Sn4Sb3 (x = 0.43) indicate that it is topologically nontrivial similar to Sb, but with different Z2 invariants (0;111). Our results not only identify a new superconducting region in the Sn-Sb phase diagram, but also provide a viable platform to study the interplay between structural modulation, nontrivial band topology and superconductivity.