Abstract-Single-Cycle Terahertz Driven Quantum Beats Reveal Symmetry-Selective Control of Excitonic Fine Structure in Perovskite

Z. Liu, C. Vaswani, X. Yang, X. Zhao, Y. Yao, Z. Song, D. Cheng, Y. Shi, L. Luo, D. H. Mudiyanselage, C. Huang, J.-M. Park, J. Zhao, Y. Yan, K.-M. Ho, J. Wang

https://arxiv.org/abs/1905.12373

Coherent time-frequency visualization reveals symmetry-selective vibronic (mixed exciton/lattice) quantum beats at cryogenic temperature after a single-cycle terahertz (THz) pumping in MAPbI3 perovskite. Above a critical threshold, a Raman phonon mode distinctly modulates the very {\em narrow}, middle region with {\em persistent} coherence for more than ten times longer than the two sides that predominately couple to infrared (IR) modes. Such spectral-temporal asymmetry and selectivity are inconsistent with a single exciton model, but in excellent agreement with a simulation of the Rashba-type, {\em three-fold} fine structure splitting of middle optically-forbidden, dark excitonic states and two bright ones, lying above and below. These hint ``Rashba engineering", i.e., periodic brightening and modulation of the spin-split excitons and Rashba parameters, by phonon symmetry and coherence.