Twinning-plane superconductivity

A new phenomenon has been discovered recently: twinning-plane superconductivity (TPS). The present paper is a survey of experimental and theoretical work on TPS. TPS arises at temperatures higher than the bulk critical temperature of a single crystal, and has a localized character. This phenomenon is caused by Cooper-pairing enhancement near the twinning plane. TPS is characterized by anomalously strong diamagnetism above the critical point. The phase (H, T) diagram of TPS is very specific and differs noticeably for type-I and type-II superconductors (e.g. tin and niobium). The interaction of closely spaced twinning planes is discussed, as well as the case of TPS in microscopic particles. The proximity effect is shown to be reduced under these conditions, and the critical temperature noticeably increased (by a factor of two to three times for tin). The prospects for further investigations of TPS are considered.