Can superconductivity survive at very low electron density? (video)

Patrick Lee, William & Emma Rogers Professor of Physics, MIT

In the standard BCS theory of superconductivity, electrons experience an attraction due to phonons and the coupling constant is proportional to the density of states. As the electron density becomes very low, so does the density of states and superconductivity is destroyed. A second requirement is the retardation of the interaction which requires the phonon frequency to be much lower than the Fermi energy.
I will examine the three record holders of low density superconductors, doped SrTiO3, YPtBi and the newly discovered superconductivity in Bi and discuss whether Nature has to go outside the standard BCS theory to superconduct at very low density.