THz-induced activation of hidden states in rare-earth-doped BiFeO3 solid solutions

An atomistic effective Hamiltonian is used to study the response of a $(\mathrm{Bi},\mathrm{Nd}){\mathrm{FeO}}_{3}$ (BNFO) solid solution to a train of THz electric field pulses. Several hidden states (i.e., states that are usually not thermodynamically accessible) with various magnitudes of the electric polarization as well as different oxygen octahedral tilting patterns and antipolar arrangements are found, which is promising for designing ultrafast neuromorprhic architectures. The occurrence of these hidden states, along with the accompanying polarization pumping, originates from the specific trilinear and biquadratic couplings between oxygen octahedral tiltings and cation displacements. Consequently, the THz-activated transformation between these different states can be thought to be a ratchet mechanism both in real and reciprocal spaces.