Josephson diode (JD) effect found in Josephson tunnel junctions (JTJs) has
attracted a great deal of attention due to its importance for developing
superconducting circuitry based quantum technologies. So far, the highly
desirable electrical control of the JD effect has not been demonstrated in any
JTJ prepared by techniques used in semiconductor industry. We report the
fabrication of JTJs featuring a composite tunnel barrier of Al$_2$O$_3$ and
Hf$_{\mathrm{0.8}}$Zr$_\mathrm{0.2}$O$_2$ prepared by
complementary-metal-oxide-semiconductor (CMOS) compatible atomic layer
deposition (ALD). These JTJs were found to show the JD effect in nominally zero
magnetic fields with the nonreciprocity controllable using an electric training
current, yielding a surprisingly large diode efficiency not achieved
previously. The quasiparticle tunneling, through which the Josephson coupling
in a JTJ is established, was found to show no nonreciprocity. We attribute
these observations to the simultaneous presence of positive and negative
Josephson couplings, with the latter originating from indirect tunneling. The
resulted spontaneous time-reversal symmetry breaking and the double-minima
washboard potential for the ensemble averaged phase difference in the
resistively and capacitively shunted junction (RCSJ) model are shown to fully
account for the experimentally observed JD effect.

Cet article explore les excursions dans le temps et leurs implications.

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