Quantum Acoustics

The flatland world of electrons residing at the two-dimensional interface between semiconductor planes is an integral part of quantum-well lasers found in many popular electro-optical devices such as grocery scanners and CD players. But the physics at work in these two dimensional electron gases (2DEG) is far from exhausted.

Two years ago a team of physicists used subtle sound waves (surface acoustic waves, or SAW) rippling through one of the semiconductor planes used to confine the electrons to form up the electrons into orderly lines (in effect "quantum wires") and also to transport controllably these formations (see Physical Review Focus).

Now the team, consisting of physicists at the Institute of Semiconductor Physics in Novosibirsk, Russia (contact Sasha Govorov, temporarily at Ohio University, govorov@helios.ohiou.edu) and the Ludwig Maximilans University in Munich (Achim Wixforth, achim.wixforth@physik.uni-muenchen.de ), propose to use two such surface acoustic waves, oriented at right angles, to confine the electrons to essentially zero-dimensional pockets which can be maneuvered around. Thus initially free electrons are organized into quantum wires and dots by intense sound waves.

Furthermore, the train of wires or dots might be able to move through the "quantum film" (the planar region between the semiconductor layers) without resistance; alternatively it can be said that the sound waves move without dissipation, thus constituting an example of self-induced acoustic transparency.

The researchers, who are presently testing their scheme, also hope to combine this ability to position electrons or deliver them selectively to quantum dots with other processes, such as the conversion of light waves into electron-hole (exciton) objects useful for processing optically-encoded information (see Update 321 and accompanying animation; and Ludwig Maximilans website). (Govorov et al., Physical Review Letters, 26 November 2001.)