Séminaire

Vendredi 31 Mars 2023 à 11h00.

Non-reciprocal transport in superconducting Nb channels

''Certain asymmetric conductors exhibit non-reciprocal transport properties, characterized by the fact that the resistance for current flow is different in opposite directions. The most well-known example of such a system is the p-n junction diode. The phenomenon of non-reciprocal transport is quite general and may be observed in systems lacking inversion symmetry. A broad range of solid-state systems, including both semiconductors and superconductors, are known to exhibit such properties. A prominent signature of non-reciprocity is the generation of a voltage signal with d.c. and even harmonic components when an a.c. current is applied.
In the case of superconducting devices, non-reciprocity may arise due to non-centrosymmetric crystal structure [1], Rashba-type spin orbit interaction [2], interface with a different material [3,4], and the presence of asymmetric pinning arrays [5,6]. In most instances, non-reciprocal behaviour is seen in the presence of an applied magnetic field, therefore requiring the absence of both inversion and time reversal symmetries. Accordingly, the voltage observed has an antisymmetric dependence on the magnetic field. It has been reported that some of these systems are capable of rectifying environmental electromagnetic fluctuations into a d.c. voltage, leading to the spontaneous generation of d.c. electricity [7,8].
We have conducted experiments with superconducting Nb films and observed the spontaneous generation of d.c. voltage resulting from the rectification of environmental fluctuations. The devices used in our experiments are not designed to be asymmetric. The rectification effect observed here can be attributed to an unconventional mechanism of non-reciprocal transport resulting from a spontaneous breaking of inversion symmetry at the superconducting transition. The unconventional nature is further confirmed by the fact that the rectified signal is symmetric with respect to the magnetic field, in stark contrast to most other systems reported in literature.
[1] R. Wakatsuki et al., Sci. Adv. 3, e1602390 (2017)
[2] Y. M. Itahashi et al., Sci. Adv. 6, eaay9120 (2020)
[3] K. Yasuda et al., Nat. Commun. 10, 2734 (2019)
[4] F. Ando et al., Nature 584, 373 (2020)
[5] J. E. Villegas et al., Science 302, 1188 (2003)
[6] C. C. de Souza Silva et al., Nature 440, 651 (2006)
[7] J. Lustikova et al., Nat. Commun. 9, 4922 (2018)
[8] E. Zhang et al., Nat. Commun. 11, 5634 (2020)
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