Srabani Kar, Van Luan Nguyen, Dipti R. Mohapatra, Young Hee Lee, A. K. Sood
http://pubs.acs.org/doi/abs/10.1021/acsnano.7b08555?journalCode=ancac3
Photoinduced terahertz conductivity Δσ(ω) of Bernal stacked bilayer graphene (BLG) with different dopings is measured by time resolved optical pump terahertz probe spectroscopy. The real part of photoconductivity Δσ(ω) (ΔσRe(ω)) is positive throughout the spectral range 0.5-2.5 THz in low doped BLG. This is in sharp contrast to Δσ(ω) for high doped bilayer graphene where ΔσRe(ω) is negative on low frequency and positive on the high frequency side. We use Boltzmann transport theory to understand quantitatively the frequency dependence of Δσ(ω), demanding the energy dependence of different scattering rates such as short-range impurity scattering, Coulomb scattering, carrier-acoustic phonon scattering, and substrate surface optical phonon scattering. We find that the short-range disorder scattering dominates over other processes. The calculated photoconductivity captures very well the experimental conductivity spectra as a function of lattice temperature varying from 300 K to 4K, without any empirical fitting procedures adopted so far in the literature. This helps to understand intraband conductivity of photo-excited hot carriers in 2D materials.
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