Polarization transfer force on ferroelectric domain walls

Abstract

We investigate the dynamics of ferroelectric textures driven by polarization currents. We show that, ferrons, the quanta of collective polarization excitations, provide an exotic driving mechanism for domain wall (DW) dynamics, compared with their magnonic counterparts. By mapping the linear polarization dynamics of a DW onto a Schrödinger-like problem with a Pöschl-Teller potential, we show that polarization waves are fully transmitted and therefore do not exert a net force on the DW in the linear regime. However, intrinsic nonlinearities give rise to a negative radiation pressure that pulls the DW toward the source. This mechanism allows efficient DW control by optical excitation and temperature gradients with application potential in ferroelectric memory and logic devices.

Figures (4)

• Figure 1: Illustration of a transverse and therefore neutral Ising wall with width $\Delta$ and polarization distribution $p$ that can be driven by a ferron current ${\bf j}_p$.
• Figure 2: (a) Dispersion relation of ferrons for the material parameters of LiNbO$_3$Para. The gray arrow indicates the second-harmonic generation (SHG) in the sample, while the green arrows denote their energy-conserving but momentum-non-conserving scattering $(2k,2\omega)\rightarrow(\pm q,2\omega)$ by the DW. (b) Wavefunction of a propagation ferron at $k=1$ rad/nm and frequency $\omega$ [black dot in (a)]. The solid and dashed curves correspond to the real and imaginary parts, respectively. (c) Amplitude of the forward [$+q$ (gray)] and backward [$-q$ (blue)] scattering states of the second-harmonic components. (d) Radiation pressure $F$ as a function of the excitation frequency $f=\omega / (2 \pi)$ and $A=0.1 p_s$. Dots mark the force at frequency $f=8,9,10$ THz, respectively.
• Figure 3: (a) Ferron dispersion in single-domain LiNbO$_3$. The color map shows the spectrum obtained by Fourier transforming the numerical results of $p(x,t)$ under broadband excitation and compares with the analytical dispersion (dashed line). (b) Spatiotemporal map of the polarization under a weak harmonic drive with frequency $f=8$ THz and amplitude $e_0=0.001$ applied at $x=-100$ nm. Insets: snapshots of the polarization dynamics to the left and right of the DW at $t=200$ ps after switching on the drive. The DW does not move in the linear regime. (c) Spatiotemporal map of the polarization under strong pumping $e_0=0.1$. (d) Polarization profiles at $t=0$ (gray) and $t=200$ ps (green). (e) Fourier amplitude of polarization fluctuations in the left (black) and right (red) domains, averaged over $t=150\sim200$ ps. In the simulations, $k=1$ rad/nm and $q=5.14$ rad/nm.
• Figure 4: (a) Time-dependent DW position for several driving field amplitudes at $f=8$ THz. Inset: DW velocity as a function of the fourth power of the ferron amplitude. The numerical (dots) and analytical [Eq. \ref{['dotX']}, solid lines] results agree well. (b) DW trajectories as a function of time for different driving frequencies at a fixed amplitude $e_0=0.1$.