Excitonic superconductivity

A brief review is given of attempts to observe an effective attractive interaction between electrons from exchange of electronic rather than phonon excitations so as to obtain superconductivity at higher temperatures than is possible from the phonon mechanism. The lack of success shows that conditions for excitonic superconductivity must be very demanding but do not rule it out completely. Greatest interest at present is on the anomalously large diamagnetism observed in cuprous chloride under pressure. (Auth.)