Parametric Amplification and Phononic Frequency Comb Generation in MoS2 Nanoelectromechanical Resonators

This paper reports on extraordinarily strong parametric amplification and spectral linewidth narrowing effects in atomically thin molybdenum disulfide (MoS
2
) resonant nanoelectromechanical systems (NEMS), by applying the electrical pump signal at local gate. It also demonstrates phononic frequency comb (PnFC) formation based on 2:1 mode coupling during the degenerate parametric amplification. For a single-layer (1L) MoS
2
resonator, we measure the displacement spectral density without and with electrical parametric pumping and calculate the parametric gain and linewidth narrowing. We observe a parametric gain as high as ~10,000 (80dB) and spectral linewidth narrowing factor of ~5000 with 153mV pump voltage at 2f. Since there is another mode present near 2f, driving the device at 2f enables mode coupling between the fundamental mode and the mode near 2f, and generates a PnFC with tunable comb spacing. The exceptional parametric amplification and spectral linewidth narrowing opens new possibilities towards building high performance atomically thin NEMS resonators for sensing applications.