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Article
mechanism, the spin-triplet Cooper pairs induced by Rashba splitting
have essential roles in the nonreciprocal charge transport and critical
current in the [Nb/V/Ta]n superlattice. Since the ratio of spin-triplet to
spin-singlet pair amplitudes is of the same order of magnitude as ER/EF
(refs.^23 ,^26 ,^27 ), we expect parity-mixing with a spin-triplet component of
approximately 1%. However, not only the spin-triplet pair amplitude but
also the spin-triplet pairing interaction is essential for the nonrecipro-
cal transport^21. The pairing interaction depends on the details of the
system^23 ,^26 –^29. Moreover, this model neglects the interband scatterings
due to multiband structure and magnetochiral anisotropy originating
from other mechanisms, such as vortex dynamics. Actually, vortices are
likely to enter along the field direction because the coherence length
of 13 nm (see Methods and Extended Data Fig. 3) is much smaller than
the thickness of 120 nm. These problems remain to be solved before we
can obtain a more accurate estimate of the pairing compositions in the
[Nb/V/Ta]n superlattice. We note that the vortex dynamics associated
with the Berezinskii–Kosterlitz–Thouless transition^13 ,^30 characteristic
of two-dimensional superconductors is unlikely to be the origin of the
nonreciprocal transport in the [Nb/V/Ta]n superlattice, because the film
is much thicker than the coherence length. Our theoretical understand-
ing of the nonreciprocal charge transport and critical current is as yet
far from complete.
In conclusion, we have demonstrated a magnetically controllable
superconducting diode in an artificial [Nb/V/Ta]n superlattice. The
nonreciprocal R–I curves, revealing the nonreciprocal critical current,
were observed using d.c. measurements, and should be related to the
magnetochiral anisotropy effect induced by the Rashba spin–orbit
interaction. This superconducting diode effect enables directional
charge transport without energy loss at low temperatures, leading to
an ultrahigh sensitivity detection circuit and a modulator with ultralow
power consumption, as opposed to the semiconductor diodes used at
present, which have high resistivity and are typically unusable at low
temperature. In addition, the performance of the superconducting
diode is expected to be easily controlled by tuning the superlattice
structure, such as the constituent elements, thickness or repetition
number. This superconducting diode should pave the way towards
the development of superconducting devices.
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© The Author(s), under exclusive licence to Springer Nature Limited 20200.7 0.8 0. 91 .00100200300400500600J (T–1A–1)T/TcFig. 4 | Magnetochiral anisotropy of the [Nb/V/Ta]n superlattice. The
coefficient of magnetochiral anisotropy γ determined from R 2 ω/Rω as a
function of temperature. Although a dip appears ref lecting the small R 2 ω at
4.2 K and 4.3 K (Fig. 3b), the plot roughly shows the trend of γ increasing in the
vicinity of Tc.