Interesting superconductivity developments

Three superconductivity-related things during the crazy end-of-semester time crunch. 

First, the paper that I'd mentioned here has been accepted and published in Nature Materials here.  That one reports signatures of superconductivity in a single atomic layer of FeSe on SrTiO₃ at around 100 K.  This result is not without controversy, as it's very hard to do standard transport in single layers of material like this in UHV, and usually people want to have multiple signatures besides resistivity when claiming superconductivity.

In that vein, there is a recent preprint that reports superconductivity above 190 K (!) in H₂S under high pressure.  The belief by the authors is that this is conventional superconductivity, related to classic work over many years (see here and here for example) by Neil Ashcroft and others discussing superconductivity in metallic hydrogen (possibly responsible for things like Jupiter's large magnetic field, for instance).  Because of the challenges of doing ultrahigh pressure measurements in diamond anvil cells, this, too, has only resistivity apparently dropping to zero as its main evidence for superconductivity.  It looks pretty cool, and it will be interesting to see where this goes from here.

Lastly, in Nature there is a paper that looks at trying to understand recent measurements of copper oxide superconductors when hit with ultrafast laser pulses.  The argument in those pump-probe experiments is that smacking the cuprates while in the normal state is enough to produce apparent transient superconductivity (as inferred on picosecond timescales with another optical pulse used to measure a quantity related to the conductivity).  The new paper claims that the initial pulse produces lattice distortions that should favor higher temperature superconductivity.

The common thread here:  There continue to be tantalizing hints of possible higher temperature superconductors, but in all of these cases it's really darn hard to do the measurements (or at least to bring multiple tools to bear).  For a nice look at this topic, see these recent words of wisdom.