We explore the ultrafast reflectivity response from photo-generated coupled phonon-surface Dirac plasmons in Sb2Te3 topological insulators several quintuple layers thick. The transient coherent phonon spectra obtained at different time frames exhibit a Fano-like asymmetric line shape of the A1g2 mode, which is attributed to quantum interference between continuum-like coherent Dirac-plasmons and phonons. By analyzing the time-dependent asymmetric line shape using the two-temperature model (TTM), it was determined that a Fano-like resonance persisted up to ≈1 ps after photo-excitation with a relaxation profile dominated by Gaussian decay at ≤200 fs. The asymmetry parameter could be well described by the TTM for ≥200 fs, therefore suggesting the coherence time of the Dirac plasmon is ≈200 fs.
@article{arxiv.1804.09308,
title = {Coherent Dirac plasmons in topological insulators},
author = {Richarj Mondal and Akira Arai and Yuta Saito and Paul Fons and Alexander V. Kolobov and Junji Tominaga and Muneaki Hase},
journal= {arXiv preprint arXiv:1804.09308},
year = {2018}
}