Terahertz acoustic phonon Cerenkov emission in bilayer graphene

Abstract

We present a theoretical investigation on the generation of Cerenkov emission of terahertz acoustic phonons in bilayer graphene (BLG) in the presence of a driving dc electric field. We have numerically and analytically studied the Cerenkov phonon emission spectrum, [Formula: see text], and phonon intensity, [Formula: see text], dependence on the phonon frequency [Formula: see text], drift velocity [Formula: see text], electron temperature [Formula: see text], concentration n, and phonon emission angle [Formula: see text] in BLG with and without considering the chirality of the charge carriers. We find that the magnitude of [Formula: see text] increases at larger drift velocities and applied electric fields with the peak of the spectrum shifting toward the higher frequency side. The spectrum magnitude in BLG is found to be much enhanced as compared to conventional 2D semiconductors and transition metal dichalcogenides, which makes it viable for SASER and other practical device applications. The chiral nature of carriers strongly influences the [Formula: see text] behavior and sharpens the spectrum peak but with a decrease in the magnitude. The chirality favors the negative emission spectrum caused by the absorption of acoustic phonons. [Formula: see text] and [Formula: see text] are found to be strongly dependent on temperature but independent of carrier concentration in the equipartition regime. The study is significant from the point of application of BLG as an acousto/optoelectronic device and high-frequency phonon spectrometers.