Comment on two papers claiming records for the lowest carrier concentration at which superconductivity has been observed
arXiv:1604.05660
Abstract
A recent paper and a preprint both claim records for the lowest carrier concentration at which superconductivity has been observed. However colleagues in Australia and I found evidence for superconductivity at concentrations of the order of at least a hundred times lower in the 1980's, in a ceramic sample of SrTiO_3 with 3% of Ti replaced by Zr.
2 pages. This will not be submitted as a comment to Phys. Rev. X as they apparently require a large payment from authors