Control of Elementary Excitations by Acoustic Fields

Acoustic waves are elastic vibrations propagating either in the bulk (bulk acoustic waves) or along the surface (surface acoustic waves, SAWs) of a solid. The latter resemble seismic waves created during earthquakes. Acoustic waves can be electrically excited using piezoelectric transducers, a technique widely used in signal processing. In this core research area, we exploit high-frequency acoustic waves for the modulation and control of semiconductor nanostructures.

The fields produced by acoustic waves induce a time- and spatial dependent modulation of the materials band structure, thus changing the band gap as well as the optical properties. In addition, acoustic waves in piezoelectric materials are accompanied by a piezoelectric field, which strongly interacts with free carriers. Moreover, due to their moving nature, acoustic fields can generate mobile potentials for the storage and transport of carriers.

Our current areas of interest include the following topics:

  • Electric generation and propagation control of GHz acoustic waves: III-V semiconductors are piezoelectric: acoustic waves can be generated using appropriate transducers. Here, we investigate materials and structures for wave generation as well as for the control of their propagation.
  • Long-range carrier and spin transport in nanostructures: We exploit the moving character of SAWs to transport and manipulate carriers and spins in nanostructures. Also included here is the development of nanostructures with long spin lifetimes required for the long-range acoustic transport.
  • Control and transport of dipolar excitons: We use for that purpose long-living dipolar (or indirect) excitons in a double quantum well structure. These excitons have strong dipolar interactions, and their long lifetimes enable transport by the moving band gap modulations produced by a SAW.
  • Acoustic control of microcavity exciton polaritons (MP): MPs are light-matter particles resulting from the strong coupling between quantum well excitons and photons in a microcavity. MPs have long spatial and temporal coherence, which can be manipulated by dynamic acoustic fields.
  • Dynamic magneto-acoustic effects: we study here the interaction between dynamic acoustic fields and magnetic excitations such as spin waves in epitaxial ferromagnetic/semiconductors.
  • Acoustic control of single emission centers: SiC as well as 2D-materials such as h-BN host defect centers, which act as single photon emitters even at room temperature and can be manipulated and controlled by acoustic waves.
Dr. Paulo Santos
+49 30 20377-221