Prediction of unexpected behavior of the mean inner potential of superconductors

•Superconductors are predicted to expel electrons from their interior to the surface.•This would result in a mean inner potential that increases with sample thickness.•It is proposed that electron holography can detect this unexpected effect.•If verified, it would change the understanding of superconductivity.

Off-axis electron holography can measure the mean inner electric potential of materials. The theory of hole superconductivity predicts that when a material is cooled into the superconducting state it expels electrons from its interior to the surface, giving rise to a mean inner potential that increases with sample thickness. Instead, in a normal metal and in a conventional BCS superconductor the mean inner potential is expected to be independent of sample thickness and temperature. Thus, this experiment can provide a definitive test of the validity of the theory of hole superconductivity.