The diode effect is fundamental to electronic devices and is widely used in rectifiers and AC-DC converters. However, conventional diodes have an energy loss due to finite resistance. We found the superconducting diode effect (SDE) in Nb/V/Ta superlattices with a polar structure, which is the ultimate diode effect exhibiting a superconducting state in one direction and a normal state in the other [1-3]. SDE can be considered as the nonreciprocity of the critical current for the metal-superconductor transition. We also found the reverse effect, i.e., the nonreciprocal critical magnetic field under the application of the supercurrent . We also found that the polarity of the superconducting diode shows a sign reversal as a magnetic field is increased, which can be considered as the crossover and phase transitions of the finite-momentum pairing states predicted theoretically . SDE in Nb/V/Ta superlattices needs an application of an external magnetic field to break the time reversal symmetry, which is a disadvantage in applications. We recently succeeded in demonstrating SDE in a zero-field by introducing ferromagnetic layers in superlattices. The polarity of the SDE is controlled by the magnetization direction of the ferromagnetic layer, leading to development of novel non-volatile memories and logic circuits with ultralow power consumption.
This work was partly supported by JSPS KAKENHI Grant Numbers (18H04225, 18H01178, 18H05227, 20H05665, 20H05159, 21K18145), the Cooperative Research Project Program of the Research Institute of Electrical Communication, Tohoku University, the Collaborative Research Program of the Institute for Chemical Research, Kyoto University, and the Russian Ministry of Science and Higher Education under Megagrant No. 075-15-2021-607.
 F. Ando et al., J. Magn. Soc. Japan 43, 17 (2019).
 F. Ando et al., Nature 584, 373 (2020).
 F. Ando et al., Jpn. J. Appl. Phys. 60, 060902 (2021).
 Y. Miyasaka et al., Appl. Phys. Express 14, 073003 (2021).
 A. Daido et al., Phys. Rev. Lett. 128, 037001 (2022)
Keywords: Superconducting Diode Effect , Rashba Superlattice