  Memristive circuit elements constitute a cornerstone for novel electronic
applications, such as neuromorphic computing, called to revolutionize
information technologies. By definition, memristors are sensitive to the
history of electrical stimuli, to which they respond by varying their
electrical resistance across a continuum of nonvolatile states. Recently, much
effort has been devoted to developing devices that present an analogous
response to optical excitation. Here we realize a new class of device, a
tunnelling photo-memristor, whose behaviour is bimodal: both electrical and
optical stimuli can trigger the switching across resistance states in a way
determined by the dual optical-electrical history. This unique behaviour is
obtained in a device of ultimate simplicity: an interface between a
high-temperature superconductor and a transparent semiconductor. The
microscopic mechanism at play is a reversible nanoscale redox reaction between
both materials, whose oxygen content determines the electron tunnelling rate
across their interface. Oxygen exchange is controlled here via illumination by
exploiting a competition between electrochemistry, photovoltaic effects and
photo-assisted ion migration. In addition to their fundamental interest, the
unveiled electro-optic memory effects have considerable technological
potential. Especially in combination with high-temperature superconductivity
which, beyond facilitating the high connectivity required in neuromorphic
circuits, brings photo-memristive effects to the realm of superconducting
electronics.
