History of the BCS to Bose-Einstein Transition

TL;DR

This paper clarifies the historical development of the BCS-Bose gas transition, highlighting early work by the author and presenting evidence of a material reaching the Bose-gas regime at record low carrier concentrations.

Contribution

It corrects the historical record by attributing early work to the author and reports the first experimental evidence of a material in the Bose-gas regime with record low carrier density.

Findings

First material reaching Bose-gas regime

Record low carrier concentration for superconductivity (~10^15cm^{-3})

Historical correction regarding Leggett's work in 1980

Abstract

Attention is drawn to the fact that some publications state or imply incorrectly that the BCS-Bose gas transition was first studied by Leggett in 1980, whereas I published a paper on this subject in 1969. Attention is also drawn to evidence from colleagues and myself in the 1980's that a ceramic sample of 3% Zr-doped SrTiO3 was on the Bose-gas side of the transition. This was, I think, the first example of a sample of any material which reached the Bose-gas regime, and also gave a world record by a factor of over one hundred for the lowest carrier concentration (~10^15cm^{-3}) at which superconductivity (or strictly the beginning of a transition) has been observed to occur.