COVID-19 herd immunity in the absence of a vaccine: an irresponsible approach.

As severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread rapidly throughout the human population, the concept of "herd immunity" has attracted the attention of both decision-makers and the general public. In the absence of a vaccine, this entails that a large proportion of the population will be infected to develop immunity that would limit the severity and/or extent of subsequent outbreaks. We argue that adopting such an approach should be avoided for several reasons.

Unraveling the flaws of estimates of the infection fatality rate for COVID-19.

The infection fatality rate (IFR) of COVID-19 is of importance for policymaking. We show that there are significant flaws in many studies estimating the IFR and used as references by public health authorities.

Coexistence of Superconductivity and Charge Density Waves in Tantalum Disulfide: Experiment and Theory.

The coexistence of charge density wave (CDW) and superconductivity in tantalum disulfide (2H-TaS_{2}) at low temperature is boosted by applying hydrostatic pressures to study both vibrational and magnetic transport properties. Around P_{c}, we observe a superconducting dome with a maximum superconducting transition temperature T_{c}=9.1  K.

Unusual effects of Be doping in the iron-based superconductor FeSe.

Recent superconducting transition temperatures (T ) over 100 K for monolayer FeSe on SrTiO have renewed interest in the bulk parent compound. In KCl:AlCl flux-transport-grown crystals of FeSeBe, FeSeBe and, for comparison, FeSe, this work reports doping of FeSe using Be-among the smallest of possible dopants, corresponding to an effective 'chemical pressure'. According to lattice parameter measurements, 6% Be doping shrank the tetragonal FeSe lattice equivalent to a physical pressure of 0.

Evolution of the Fermi surface of BiTeCl with pressure.

We report measurements of Shubnikov-de Haas oscillations in the giant Rashba semiconductor BiTeCl under applied pressures up to  ∼2.5 GPa. We observe two distinct oscillation frequencies, corresponding to the Rashba-split inner and outer Fermi surfaces.

Pressure-induced superconductivity in the giant Rashba system BiTeI.

At ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur.

Pressure tuning the Fermi level through the Dirac point of giant Rashba semiconductor BiTeI.

We report measurements of Shubnikov-de Haas oscillations in the giant Rashba semiconductor BiTeI under applied pressures up to ∼2 GPa. We observe one high frequency oscillation at all pressures and one low frequency oscillation that emerges between ∼0.3-0.