Femtosecond time-evolution of mid-infrared spectral line shapes of Dirac fermions in topological insulators

Tien Tien Yeh*, Chien-Ming Tu, Wen Hao Lin, Cheng Maw Cheng, Wen Yen Tzeng, Chen Yu Chang, Hideto Shirai, Takao Fuji, Raman Sankar, Fang Cheng Chou, Marin M. Gospodinov, Takayoshi Kobayashi, Chih-Wei Luo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Mid-infrared (MIR) light sources have much potential in the study of Dirac-fermions (DFs) in graphene and topological insulators (TIs) because they have a low photon energy. However, the topological surface state transitions (SSTs) in Dirac cones are veiled by the free carrier absorption (FCA) with same spectral line shape that is always seen in static MIR spectra. Therefore, it is difficult to distinguish the SST from the FCA, especially in TIs. Here, we disclose the abnormal MIR spectrum feature of transient reflectivity changes (ΔR/R) for the non-equilibrium states in TIs, and further distinguish FCA and spin-momentum locked SST using time-resolved and linearly polarized ultra-broadband MIR spectroscopy with no environmental perturbation. Although both effects produce similar features in the reflection spectra, they produce completely different variations in the ΔR/R to show their intrinsic ultrafast dynamics.

Original languageAmerican English
Article number9803
Pages (from-to)1-8
Number of pages8
JournalScientific reports
Volume10
Issue number1
DOIs
StatePublished - 17 Jun 2020

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