Graphene heat engine*

Nano-electromechanical systems (NEMS) have become an important platform in recent times for applications of nonlinear and non-equilibrium phenomena [1]. Recently, it has been demonstrated that squeezed states of NEMS modes can be used as two heat baths to construct a Carnot cycle towards development of a nano-mechanical heat engine [2]. With two quadratures acting as two temperature baths, practical applications of such  heat engines can be challenging, since it is often difficult to phase sensitivity couple one mode of system to the engine. Here we propose using a novel scheme of parametrically driving graphene resonators [3], at a frequency which is an order of magnitude lower than the fundamental mode of graphene.  With increasing drive strength, we find generation of sideband on the Thermal mode of graphene, cooling down the mode to 51 K. Furthermore, we find that with sudden turn-off of the drive, the temperature equilibrates at a time scale which is orders of magnitude faster than the time scale over which the frequency of the fundamental graphene modes shift. We use the shifted frequency, along with changing thermal phonons as two paths to close a Carnot cycle that operates with an efficiency of 83%. Dispersion of graphene allows us to switch the sense of direction of the cycles, thereby converting the engine to a refrigerator. We expect these results to be applicable in a wide range of nano-scale devices which seeks efficient conversion from thermal phonons to mechanical work at rf frequencies.