Cerenkov emission of terahertz acoustic-phonons from graphene

摘要

We present a theoretical study of the electrical generation of acoustic-phonon emission from graphene at room temperature. The drift velocity (v_x) and temperature of electrons driven by dc electric field (F_x) are determined by solving self-consistently the momentum- and energy-balance equations derived from the Boltzmann equation. We find that in the presence of impurity, acoustic- and optic-phonon scattering, v_x can be much larger than the longitudinal (v_l) and transverse (v_t) sound velocities in graphene even within the linear response regime. As a result, although the acoustic Cerenkov effect cannot be obviously seen in the analytical formulas, the enhanced acoustic-phonon emission can be observed with increasing F_x when v_x ＞ v_l and v ＞ v_t. The frequency of acoustic-phonon emission from graphene can be above 10 THz, which is much higher than that generated from conventional semiconductor systems. This study is pertinent to the application of graphene as hypersonic devices such as terahertz sound sources.