Gate Tunable Cooperativity between Vibrational Modes.

Coupling between a mechanical resonator and optical cavities, microwave resonators, or other mechanical resonators have been used to observe interesting effects from sideband cooling to coherent manipulation of phonons. Here we demonstrate strong coupling between different vibrational modes of MoS2 drum resonators at room temperature. We observe intermodal as well as intramodal coupling. Cooperativity, a measure of coupling between the two modes, can be tuned by more than an order of magnitude by changing the direct current gate bias. The large measured cooperativity of about 900 at room temperature indicates that the phonon population can be coherently transferred between the modes for more than 500 cycles. This coherent oscillation is of great interest in studying quantum effects in macroscopic objects.

The effect of strain on effective Duffing nonlinearity in the CVD-MoS2 resonator.

We demonstrate all electrical measurements on NEMS devices fabricated using CVD grown monolayer MoS2. The as-grown monolayer film of MoS2 on top of the SiO2/Si wafer is processed to fabricate arrays and individual NEMS devices without the complex pick and transfer techniques associated with graphene. The electromechanical properties of the devices are on par with those fabricated using the exfoliation method. The frequency response of these devices is then used as a probe to estimate the linear thermal expansion coefficient of the material and evaluate the effect of strain on the effective Duffing nonlinearity in the devices.

Parametric amplification in MoS2 drum resonator.

Parametric amplification is widely used in diverse areas from optics to electronic circuits to enhance low level signals by varying relevant system parameters. Parametric amplification has also been performed in several micro-nano resonators including nano-electromechanical system (NEMS) resonators based on a two-dimensional (2D) material. Here, we report the enhancement of mechanical response in a MoS2 drum resonator using degenerate parametric amplification. We use parametric pumping to modulate the spring constant of the MoS2 resonator and achieve a 10 dB amplitude gain. We also demonstrate quality factor enhancement in the resonator with parametric amplification. We investigate the effect of cubic nonlinearity on parametric amplification and show that it limits the gain of the mechanical resonator. Amplifying ultra-small displacements at room temperature and understanding the limitations of the amplification in these devices is key for using these devices for practical applications.