Electron Dynamics Reconstruction and Nontrivial Transport by Acoustic Waves

Abstract

Surface acoustic waves (SAWs) become a popular driving source in modern condensed matter physics, but most existing theories simplify them as electric fields and ignore the non-uniform Brillouin zone folding effect. We develop a semiclassical framework and reconstruct the electron dynamics by treating SAW as a quasi-periodic potential modulating electronic momentum distribution. This framework naturally explains the experimentally observed DC drag current and predicts acousto-electric Hall effect. The theory further reveals various SAW-driven transport phenomena, emerging anomalous Hall, thermal Hall, and Nernst effects within time-reversal symmetric systems. Illustrated in bilayer graphene and $\mathrm{MX_2}$ (M = Mo, W; X = S, Se, Te), the angular-dependent acousto-electric Hall effect provides an experimental probe for Berry curvature distribution.

Figures (2)

• Figure 1: (a) In the SAW system, electrons with momentum satisfying $\alpha\boldsymbol{k}_{\parallel}= \boldsymbol{C}$ become strongly bound in the potential valleys of the SAW-induced electric potential $V(\boldsymbol{x}, t)$. (b) Bottom panel: Brillouin zone and Berry curvature for a system with time reversal symmetry, resulting in Hall conductivity $\sigma_{xy}=0$. Top panel: The Brillouin zone undergoes SAW-induced non-uniform folding. The dominant contribution arises from the region near the specific momentum $\boldsymbol{k}_{\parallel} = \boldsymbol{C}/\alpha$, while contribution of other momenta diminish significantly. Non-zero $\sigma_{xy}$ is obtained.
• Figure 2: (a) Measurement setup for the angular-dependent acousto-electric Hall effect using interdigital transducers (IDTs) to generate SAW, with atomic sites A (red dots) and B (blue dots) explicitly labeled. The SAW propagation direction is defined as 0 radians along the armchair direction (A$\rightarrow$B, blue IDTs) and $\pi/3$ along an inequivalent armchair direction (B$\rightarrow$A, red IDTs). The angular dependence of the acousto-electric Hall conductivity $\sigma^a_{xy}$ is shown for (b) bilayer graphene and (c) $\mathrm{MX_2}$ systems. The calculations adopt the following SAW parameters: phase velocity $C=3000$m/s, frequency $\omega=500$MHz and input power $P_0=0.001\mu$W.