Field-free superconducting diode effect in noncentrosymmetric superconductor/ferromagnet multilayers

Abstract

The diode effect is fundamental to electronic devices and is widely used in rectifiers and AC-DC converters. At low temperatures, however, conventional semiconductor diodes possess a high resistivity, which yields energy loss and heating during operation. The superconducting diode effect (SDE) 1-8 , which relies on broken inversion symmetry in a superconductor may mitigate this obstacle: in one direction a zero-resistance supercurrent can flow through the diode, but for the opposite direction of current flow, the device enters the normal state with ohmic resistance. The application of a magnetic field can induce SDE inNb/V/Ta superlattices with a polar structure 1,2 , in superconducting devices with asymmetric patterning of pinning centres 9 , or in superconductor/ferromagnet hybrid devices with induced vortices 10,11 . The need for an external magnetic field limits their practical application. Recently, a field-free SDE was observed in a NbSe2/Nb3Br8/NbSe2 junction, and it originates from asymmetric Josephson tunneling that is induced by the Nb3Br8 barrier and the associated NbSe2/Nb3Br8 interfaces 12 . Here, we present another implementation of zero-field SDE using noncentrosymmetric [Nb/V/Co/V/Ta]20 multilayers. The magnetic layers provide the necessary symmetry breaking and we can tune the SDE by adjusting the structural parameters, such as the constituent elements, film thickness, stacking order, and number of repetitions. We control the polarity of the SDE through the magnetization direction of the ferromagnetic layers. Artificially stacked structures 13-18 , as the one used in this work, are of particular interest as they are compatible with microfabrication techniques and can be integrated with devices such as Josephson junctions 19-22 . Energy-loss-free SDEs as presented in this work may therefore enable novel non-volatile memories and logic circuits with ultralow power consumption.

Josephson Effect in NbS2 van der Waals Junctions

“…It is interesting to point out that both the switching current and retrapping current can be asymmetric, and the asymmetry is larger than the fluctuation of I s (the results of other junctions are shown in Figure S4, and the switching current statistics of JJ3 can be found in Figure S3). This observation might be caused by the superconducting diode effect (SDE) 18,19 or the self-field effect arising from the superconducting electrodes. 20−22 However, for our NbS 2 Josephson junctions, the asymmetry is insensitive to the out-of-plane magnetic field, which contrary to the predicted behavior of SDE arising from Ising spin−orbit coupling (the dominate type spin−orbit coupling in NbS 2 ).…”

Reconfigurable magnetic-field-free superconducting diode effect in multi-terminal Josephson junctions

“…Therefore, careful engineering of the interplay between spin-orbit interactions, topological phases, and magnetic fields can lead to the observation of the SDE. To this point, the SDE has been experimentally reported in a multitude of systems including but not limited to: non-centrosymmetric superconductors with the magneto-chiral anisotropy (17,18,19,20,21), Josephson junctions (JJs) based on Dirac semimetals with finite-momentum Cooper pairing (22), two-dimensional (2D) van der Waals heterostructures (23,21,24,25,26), three-terminal JJs based on InAs in the presence of a magnetic field (27), and a network of graphene JJs (28).…”

Non-Reciprocal Supercurrents in a Field-Free Graphene Josephson Triode

“…While these studies have followed a decade-long explorations of non-reciprocal supercurrents [9][10][11][12][13][14][15][16][17][18][19], the recent interest is driven by the search of novel materials which break both the inversion and time-reversal symmetry, thereby intrinsically enabling the superconducting diode effect (SDE). Such materials have indeed been experimentally identified and investigated, ranging from metallic films and proximitized semiconductors to van der Waals heterostructures [20][21][22][23][24][25][26][27][28][29][30]. While this direction offers a probe into the symmetry properties of novel materials, the resulting devices typically have limited diode efficiency, which is defined as a ratio of supercurrent in the forward and backward directions.…”