Using acoustic waves to induce high-frequency current oscillations in superlattices

TL;DR

This paper demonstrates how GHz acoustic waves in semiconductor superlattices can induce and control high-frequency electron oscillations and collective current behaviors, revealing a transition from wave dragging to Bloch oscillations.

Contribution

It introduces a novel mechanism where acoustic waves induce THz electron dynamics and self-sustained current oscillations in superlattices, highlighting the transition between different oscillation regimes.

Findings

Below threshold, electrons exhibit THz drifting orbits.

Above threshold, Bloch-like oscillations cause negative differential velocity.

Acoustic waves induce propagating electron density regions and current oscillations.

Abstract

We show that GHz acoustic waves in semiconductor superlattices can induce THz electron dynamics that depend critically on the wave amplitude. Below a threshold amplitude, the acoustic wave drags electrons through the superlattice with a peak drift velocity overshooting that produced by a static electric field. In this regime, single electrons perform drifting orbits with THz frequency components. When the wave amplitude exceeds the critical threshold, an abrupt onset of Bloch-like oscillations causes negative differential velocity. The acoustic wave also affects the collective behavior of the electrons by causing the formation of localised electron accumulation and depletion regions, which propagate through the superlattice, thereby producing self-sustained current oscillations even for very small wave amplitudes. We show that the underlying single-electron dynamics, in particular the transition between the acoustic wave dragging and Bloch oscillation regimes, strongly influence the spatial distribution of the electrons and the form of the current oscillations. In particular, the amplitude of the current oscillations depends non-monotonically on the strength of the acoustic wave, reflecting the variation of the single-electron drift velocity.