Photonics and Optoelectronics Group
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Direct observation, how Fröhlich polarons form in time

22.12.2025

We have observed that within 200 femtoseconds photoexcited electrons in BiOI nanoplatelets become heavier and experience an energetic drop of their band. As predicted by H. Fröhlich in 1954 the electron deforms the nearby lattice and creates a more immobile quasiparticle termed “polaron”. To this end time- and momentum-resolved photoemission electron microscopy experiments with 50-fs laser pulses were performed in collaboration with the group of Prof. Zhi-Heng Loh at Nanyang Technical University (NTU) in Singapore.
Read more in our latest article published in Physical Review Materials: M. Kestler, K. Woo, J. Lim, L. Prins, J. Feldmann, Z. Loh