Screening ineffectiveness and THz emission at bare LO phonon frequencies
Abstract
Within a hydrodynamic approach we investigate the dynamics of an inhomogeneous electron-hole gas coupled to phonons in Te and the corresponding THz emission. We find that the longitudinal inhomogeneity of the photogenerated electron-hole gas -- due to short absorption lengths in Te -- gives rise to screening ineffectiveness for non-zero wave-vector modes. This allows for THz dynamics and emission at the bare LO phonon frequency nuLO even at high carrier densities. Screening ineffectiveness thus provides an appealingly simple explanation for the existence of bare modes at nuLO in longitudinally inhomogeneous systems such as Te; no lateral inhomogeneity of the excitation spot is needed here.
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