Tuning the structure of organic–inorganic perovskites by pressure holds great promise for discovering materials with favorable properties. However, most of their high-pressure structures cannot be preserved at ambient conditions and little is known about how to control the properties of these materials recovered from high pressure. Here, we have manipulated the bandgap in a high-pressure-treated 2D organic-inorganic halide perovskite. We find that the bandgap of this compound can be largely altered by pressure-induced lattice disorder. Below 25 GPa, the phase transition is reversible and the thus-produced lattice distortion cannot be preserved after pressure release. In contrast, for the sample treated above 25 GPa, the structural disorder can be preserved at ambient pressure. Consequently, the bandgap of the sample can be profoundly tuned from 2.98 to 3.46 eV. These findings offer an extraordinary example for manipulating the structure and electronic properties of organic–inorganic perovskites by high pressure treatment.

The importance of type-II superconductors with strong pinning comes from their ability to carry large electrical currents in the presence of a magnetic field. We report on the results of the bulk magnetization measurements in the superconducting state in high-quality single crystals of BaFe 2−x Ni x As 2 at various doping levels ranging from the underdoped to the overdoped regimes. The zero-temperature superconducting critical current density J c at optimal composition x = 0.10, where the superconducting transition temperature T c reaches a maximum of 19.9(0.4) K, displays a pronounced sharp peak in the doping dependence. Thus the observed doping dependence of the critical current implies that pinning becomes stronger upon initial doping. In addition, the best pinning conditions are realized in the presence of structural and magnetic domains. Our results strongly suggest that the high J c values are mainly due to collective (weak) pinning of vortices by dense microscopic point defects with some contribution from a strong pinning mechanism. The experimental results of the normalized J c present a remarkably good agreement with the δl pinning theoretical curve, confirming that pinning in our samples originates from spatial variations of the charge carrier mean free path leading to small bundle vortex pinning by randomly distributed (weak) pinning centers for H c.

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The infection fatality rate (IFR) of COVID-19 is one of the measures of disease impact that can be of importance for policy making. Here we show that many of the studies on which these estimates are based are scientifically flawed for reasons which include: nonsensical equations, unjustified assumptions, small sample sizes, non-representative sampling (systematic biases), incorrect definitions of symptomatic and asymptomatic cases (identified and unidentified cases), typically assuming that cases which are asymptomatic at the time of testing are the same as completely asymptomatic (never symptomatic) cases. Moreover, a widely cited meta-analysis misrepresents some of the IFR values in the original studies, and makes inappropriate duplicate use of studies, or the information from studies, so that the results that are averaged are not independent from each other. The lack of validity of these research papers is of particular importance in view of their influence on policies that affect lives and well-being in confronting a worldwide pandemic.