  Smart electronic circuits that support neuromorphic computing on the hardware
level necessitate materials with memristive, memcapacitive, and
neuromorphic-like functional properties; in short, the electronic response must
depend on the voltage history, thus enabling learning algorithms. Here we
demonstrate volatile ferroelectric switching of Sn$_2$P$_2$S$_6$ at room
temperature and see that initial polarization orientation strongly determines
the properties of polarization switching. In particular, polarization switching
hysteresis is strongly imprinted by the original polarization state, shifting
the regions of non-linearity toward zero-bias. As a corollary, polarization
switching also enables effective capacitive switching, approaching the
sought-after regime of memcapacitance. Landau-Ginzburg-Devonshire simulations
demonstrate that one mechanism by which polarization can control the shape of
the hysteresis loop is the existence of charged domain walls decorating the
periphery of the repolarization nucleus. These walls oppose the growth of the
switched domain and favor back-switching, thus creating a scenario of
controlled volatile ferroelectric switching. Although the measurements were
carried out with single crystals, prospectively volatile polarization switching
can be tuned by tailoring sample thickness, domain wall mobility and electric
fields, paving way to non-linear dielectric properties for smart electronic
circuits.
