Anomalously slow coherent phonon dephasing in mixed-cation halide perovskites
Alex Barker a
a Istituto Italiano di Tecnologia - IIT
Oral, Alex Barker, presentation 066
Publication date: 25th November 2019

Ultra-short optical pulses (whether below-bandgap/non-resonant or above-bandgap/resonant) can impulsively generate vibrational coherences. The effect of these coherent nuclear motions on the transmission of an optical probe pulse allows us to track their evolution in time – a class of techniques referred to as Impulsive Vibrational Spectroscopy (IVS).

IVS has several advantages over continuous-wave Raman spectroscopy that are relevant to metal halide perovskites (beyond time resolution), including: sensitivity to scattering at low wavenumber without interference from the excitation light, and background-free detection being unaffected by highly luminescent samples.

We apply IVS to a series of lead and tin halide perovskites, finding an incredible disparity in the  dephasing time of vibrational coherences, suggesting that altering the sample composition can drastically change the dominant phonon scattering mechanisms at play in these materials. Additionally, the appearance of modes not typically observed in cw-Raman spectroscopy presents an interesting puzzle, and one that I would enjoy discussing with those present at the NIPHO 2020.

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