Spectroscopy

Quantum mechanics

Chemical physics

Polaron

Materials science

Social psychology

Scattering

Excitation

Phonon

Inorganic chemistry

Laser

Physics

Nanotechnology

Psychology

Optics

Molecular physics

Relaxation (psychology)

Characterization (materials science)

Condensed matter physics

Chemistry

Electron

Nanoscopic scale

Femtosecond

Optoelectronics

Halide

Nature Materials

Excitation localization involving dynamic nanoscale distortions is a central aspect of photocatalysis, quantum materials and molecular optoelectronics. Experimental characterization of such distortions requires techniques sensitive to the formation of point-defect-like local structural rearrangements in real time. Here, we visualize excitation-induced strain fields in a prototypical member of the lead halide perovskites via femtosecond resolution diffuse x-ray scattering measurements. This enables momentum-resolved phonon spectroscopy of the locally-distorted structure and reveals radially-expanding nanometer-scale elastic strain fields associated with the formation and relaxation of polarons in photoexcited perovskites. Quantitative estimates of the magnitude and the shape of this polaronic distortion are obtained, providing direct insights into the debated dynamic structural distortions in these materials. Optical pump-probe reflection spectroscopy corroborates these results and shows how these large polaronic distortions transiently modify the carrier effective mass, providing a unified picture of the coupled structural and electronic dynamics that underlie the unique optoelectronic functionality of the hybrid perovskites.

Visualization of dynamic polaronic strain fields in hybrid lead halide perovskites