Chaos

Introduction

• Developement and study of nanomechanical heat engines which converts thermal energy into mechanical work on a nanoscale, can provide crucial insights into fundamental principles of thermodynamics at the nanoscale and have potential applications for the advancement in nanotechnology ranging from nanoscale sensors, actuators, and energy-efficient computing. Various works have demonstrated that a bunch of harmonic oscillators can be used as working substance of a heat engine. 

• We observe emergence of novel non-equilibrium steady state when the system is driven with a frequency red detuned by an order of magnitude from the fundamental frequency of graphene-SiNx hybridized mode. We observe a shift in fundamental mode frequency with reduction in thermal phonon number which occurs at different timescales. We show that these intriguing characteristics of low-frequency modulation can lead to design a cyclic process that allows for extraction of mechanical work out of resonator modes. Interestingly, we observe that frequency tunability of suspended graphene membranes via tuning strain allows both way operation of the engine cycle, thereby can be used to operate the system both as heat engine and a refrigerator.

•  Calculations show that the efficiency of the engine solely depends on and increases linearly with increasing frequency tunability. So by engineering membranes which has smaller fundamental mode frequency and larger frequency tunability rate (which depends on the initial in-build strain), efficiency of the engine can be increased.