Strontium intercalation between van der Waals bonded layers of topological insulator Bi 2 Se 3 is found to induce superconductivity with a maximum T c of 2.9 K. Transport measurement on single crystal of optimally doped sample Sr 0.1 Bi 2 Se 3 shows weak anisotropy ( 1.5) and upper critical field H c2 (0) Superconductors derived from topological insulating phases of quantum matter are amongst the most profound developments of recent past.

Band gap engineering offers tunable optical and electronic properties of semiconductors in the development of efficient photovoltaic cells and photocatalysts. Our study demonstrates the band gap engineering of ZnO nanorods to develop a highly efficient visible-light photocatalyst. We engineered the band gap of ZnO nanorods by introducing the core/shell geometry with Ag2S sensitizer as the shell. Introduction of the core/shell geometry evinces great promise for expanding the light-harvesting range and substantial suppression of charge carrier recombination, which are of supreme importance in the realm of photocatalysis. To unveil the superiority of Ag2S as a sensitizer in engineering the band gap of ZnO in comparison to the Cd-based sensitizers, we also designed ZnO/CdS core/shell nanostructures having the same shell thickness. The photocatalytic performance of the resultant core/shell nanostructures toward methylene blue (MB) dye degradation has been studied. The results imply that the ZnO/Ag2S core/shell nanostructures reveal 40- and 2-fold enhancement in degradation constant in comparison to the pure ZnO and ZnO/CdS core/shell nanostructures, respectively. This high efficiency is elucidated in terms of (i) efficient light harvesting owing to the incorporation of Ag2S and (ii) smaller conduction band offset between ZnO and Ag2S, promoting more efficient charge separation at the core/shell interface. A credible photodegradation mechanism for the MB dye deploying ZnO/Ag2S core/shell nanostructures is proposed from the analysis of involved active species such as hydroxyl radicals (OH(•)), electrons (e(-)(CB)), holes (h(+)(VB)), and superoxide radical anions (O2(•-)) in the photodegradation process utilizing various active species scavengers and EPR spectroscopy. The findings show that the MB oxidation is directed mainly by the assistance of hydroxyl radicals (OH(•)). The results presented here provide new insights for developing band gap engineered semiconductor nanostructures for energy-harvesting applications and demonstrate Ag2S to be a potential sensitizer to supersede Cd-based sensitizers for eco-friendly applications.

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We report on the superconducting gap and pairing symmetry in layered superconductor Bi 4 O 4 S 3 . The measurement of temperature dependence of magnetic penetration depth was carried out using tunnel diode oscillator technique. It is observed that Bi 4 O 4 S 3 is a conventional s-wave type superconductor with fully developed gap. The zero-temperature value of the superconducting energy gap Δ 0 was found to be 1.54 meV, corresponding to the ratio 2Δ 0 /k B T c =7.2 which is much higher than the BCS value of 3.53. In the superconducting range, superfluid density is very well described by single gap s-wave model.