Ultrafast Neuromorphic Dynamics Using Hidden Phases in the Prototype of Relaxor Ferroelectrics

Materials possessing multiple states are promising to emulate synaptic and neuronic behaviors. Their operation frequency, typically in or below the GHz range, however, limits the speed of neuromorphic computing. Ultrafast THz electric field excitation has been employed to induce nonequilibrium states of matter, called hidden phases in oxides. One may wonder if there are systems for which THz pulses can generate neuronic and synaptic behavior, via the creation of hidden phases. Using atomistic simulations, we discover that relaxor ferroelectrics can emulate all the key neuronic and memristive synaptic features. Their occurrence originates from the activation of many hidden phases of polarization order, resulting from the response of nanoregions to THz pulses. Such phases further possess different dielectric constants, which is also promising for memcapacitor devices.

Figure 1

Temporal evolution of the electrical polarization (a) and corresponding snapshots of the dipole patterns (b)–(d) in PMN at 10 K subject to a single pulse of the electric field (shown in panel (a) with the parameters $E_0=4\sqrt{3}\times {10}^7\mathrm{V}/\mathrm{m}$, $\mathrm{\Delta }=0.2\mathrm{ps}$, and $\nu =\omega /2\pi =1.5\mathrm{THz}$ in Eq. (1). The arrows in panels (b)–(d) show the local electric dipoles and the red lines delimit polar nanoregions at these snapshots.

Figure 2

(a) Temporal evolution of the polarization subject to a train of pulses separated by 4 ps [the other parameters of the pulses are the same as in Fig. 1]; (b) the same as (a), but with a separation of the pulses by 6 ps; (c) Percolation strength as a function of time, for the train of pulses corresponding to panel (a); (d)–(f) $z$ component of the polarization subject to the train of pulses shown in panel (a) at different times (note that the $z$ axis is along the [111] pseudocubic direction).

Figure 3

Multiple nonvolatile polarization states (in magenta color) found at different times for the case of the train of the electric field pulses shown in Fig. 2. The lines shown with the other colors were found under no-field condition, after turning off the field at the times marked by arrows of the same color in this figure.