Intrinsic loss due to unstable modes in graphene

The mechanism of dissipation operative at the nanoscale remains poorly understood for most cases. In this work, using molecular dynamics simulations, we show that the unstable out-of-plane mode leads to the absorption of energy from the in-plane motion in graphene. The in-plane vibration modulates the potential energy profile for the out-of-plane modes. For the fundamental out-of-plane mode in the loading direction, the minimum of the potential energy shifts because of in-plane compressive strain. The structure takes a finite amount of time to relax to the new potential energy configuration. A hysteresis in the out-of-plane dynamics is observed when the time period of in-plane excitation becomes comparable to the time required for this relaxation. Increasing the stiffness of the out-of-plane modes by giving an initial tensile strain leads to a considerable decrease in dissipation rate.