Illustration of the exciton of TiO2 interacting with a propagating coherent acoustic wave. Credit: Adriel Dominguez (Max Planck Institute, Hamburg)
Physicists from Switzerland, Germany, and France have found that large-amplitude acoustic waves, launched by ultrashort laser pulses, can dynamically manipulate the optical response of semiconductors. One of the main challenges in materials science research is to achieve high tunability of the optical properties of semiconductors at room temperature. These properties are governed by "excitons", which are bound pairs of negative electrons and positive holes in a semiconductor. Excitons have become increasingly important in optoelectronics and the last years have witnessed a surge in the search for control parameters - temperature, pressure, electric and magnetic fields - that can tune excitonic properties. However, moderately large changes have only been achieved under equilibrium conditions and at low temperatures. Significant changes at ambient temperatures, which are important for applications, have so far been lacking. This has now just been achieved in the lab of Majed Chergui at EPFL within the Lausanne Centre for Ultrafast Science , in collaboration with the theory groups of Angel Rubio (Max-Planck Institute, Hamburg) and Pascal Ruello (Université de Le Mans).
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