Ultrafast atomic-scale visualization of acoustic phonons generated by optically excited quantum dots
Understanding the dynamics of atomic vibrations confined in quasi-zero dimensional systems is crucial from both a fundamental point-of-view and a technological perspective. Using ultrafast electron diffraction, we monitored the lattice dynamics of GaAs quantum dots—grown by Droplet Epitaxy on AlGaAs—with sub-picosecond and sub-picometer resolutions. An ultrafast laser pulse nearly resonantly excites a confined exciton, which efficiently couples to high-energy acoustic phonons through the deformation potential mechanism. The transient behavior of the measured diffraction pattern reveals the nonequilibrium phonon dynamics both within the dots and in the region surrounding them. The experimental results are interpreted within the theoretical framework of a non-Markovian decoherence, according to which the optical excitation creates a localized polaron within the dot and a travelling phonon wavepacket that leaves the dot at the speed of sound. These findings indicate that integration of a phononic emitter in opto-electronic devices based on quantum dots for controlled communication processes can be fundamentally feasible.
Additional Information© Author(s) 2017. All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Published Online: August 2017 Accepted: July 2017. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research in the Center for Physical Biology at Caltech supported by the Gordon and Betty Moore Foundation. J.H. acknowledges the support from China 1000-Young Talents Plan. G.M.V. acknowledges the support from the EPFL fellowship program co-funded by Marie Skłodowska-Curie. W.L. would like to acknowledge the support by the Director Fund of WNLO (Grant No. WNLOZZYJ1501) and the National Natural Science Foundation of China (Grant No. 11574094).
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