Control of Elementary Excitations (Photons, Electrons, Spins, Magnetic Flux) by Acoustic Fields

Acoustic waves are elastic vibrations propagating within the bulk (normally denoted as bulk acoustic waves) or along the surface (surface acoustic wave - SAWs) of a solid. In piezoelectric materials (like, for instance, GaAs), these waves can be electrically generated through the inverse piezoelectric effect. In the case of SAWs, the application of a microwave voltage to an interdigital transducer (IDT) deposited on the surface excites an elastic wave with wavelength corresponding the IDT period. In general, a SAW carries both a strain and a piezoelectric field, which modulate the physical properties of the underlying medium within a depth corresponding to one SAW wavelength. The modulation can be tuned by changing the SAW amplitude and is periodic both in space and time.

The figure shows the spatial distribution of a strainfield of a SAW propagating along x. The displacement u is maximum at the surface and decays with increasing depth.

This core research area aims at the use of these tunable acoustic fields to control elementary excitations (such as electrons, spins, excitons, and magnetic fluxes) in semiconductors and superconductors. An advantage of this dynamic over static modulation is - besides tunability - the control of the materials properties without introducing additional interfaces, which are normally deleterious for the electronic properties. The studies give insight into the fundamental processes governing the modulation and open perspective to develop new concepts for information storage and processing using acoustic fields. The research in this area is divided into the following subtopics:

-         generation and control of high-frequency acousto-electric vibrations in thin films,

-         dynamic photon control using acoustic fields in semiconductor nanostructures

-         transport and manipulation of electronic and magnetic objects in thin films.