Clarifying ultrafast carrier dynamics in ultrathin films of the topological insulator Bi2Se3 using transient absorption spectroscopy
arXiv:2012.13092 · doi:10.1021/acsphotonics.1c00115
Abstract
Ultrafast carrier dynamics in the topological insulator Bi2Se3 have recently been intensively studied using a variety of techniques. However, we are not aware of any successful experiments exploiting transient absorption (TA) spectroscopy for these purposes. Here we demonstrate that if the ~730 nm wavelength pumping (~1.7 eV photon energy) is applied to ultrathin Bi2Se3 films, TA spectra cover the entire visible region, thus unambiguously pointing to two-photon excitation (~3.4 eV). The carrier relaxation dynamics is found to be governed by the polar optical phonon cascade emission occurring in both the bulk states and the Dirac surface states (SS), including SS-bulk-SS vertical electron transport and being also exclusively influenced by whether the Dirac point is presented between the Dirac cones of the higher energy (~1.5 eV) Dirac SS (known as SS2). We have recognized that SS2 act as a valve substantially slowing down the relaxation of electrons when the gap between Dirac cones exceeds the polar optical phonon and resonant defects energies. The resulting progressive accumulation of electrons in the gapped SS2 becomes detectable through the inverse bremsstrahlung type free carrier absorption.
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Cited by in corpus (6)
- Coherent surface-to-bulk vibrational coupling in the 2D topologically trivial insulator Bi2Se3 monitored by ultrafast transient absorption spectroscopy
- Dynamic Opening of a Gap in Dirac Surface States of the Thin-Film 3D Topological Insulator Bi2Se3 Driven by the Dynamic Rashba Effect
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- Ultrafast transient absorption spectroscopy of 2D semiconductors: a review
- Two-photon IR pumped UV-Vis transient absorption spectroscopy of Dirac fermions in the 2D and 3D topological insulator Bi2Se3
- Anisotropic ultrafast spin/valley dynamics in WTe2 films