Nonequilibrium Thermodynamics of Acoustic Phonons in Suspended Graphene

Abstract

Recent theory has predicted large temperature differences between the in-plane (LA and TA) and out-of-plane (ZA) acoustic phonon baths in locally-heated suspended graphene. To verify these predictions, and their implications for understanding the nonequilibrium thermodynamics of 2D materials, experimental techniques are needed. Here, we present a method to determine the acoustic phonon bath temperatures from the frequency-dependent mechanical response of suspended graphene to a power modulated laser. The mechanical motion reveals two counteracting contributions to the thermal expansion force, that are attributed to fast positive thermal expansion by the in-plane phonons and slower negative thermal expansion by the out-of-plane phonons. The magnitude of the two forces reveals that the in-plane and flexural acoustic phonons are at very different temperatures in the steady-state, with typically observed values of the ratio $\Delta T_{\mathrm{LA}+\mathrm{TA}}/\Delta T_{\mathrm{ZA}}$ between 0.2 and 3.7. These deviations from the generally used local thermal equilibrium assumption ($\Delta T_{\mathrm{LA}+\mathrm{TA}}=\Delta T_{\mathrm{ZA}}$) can affect the experimental analysis of thermal properties of 2D materials.

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Cited by in corpus (6)

• Mesoscopic physics of nanomechanical systems
• Dynamics of 2D Material Membranes
• Squeeze-film effect on atomically thin resonators in the high-pressure limit
• Tuning dissipation dilution in 2D material resonators by MEMS-induced tension
• Phonon Scattering at Kinks in Suspended Graphene
• Nanomechanical vibrational response from electrical mixing measurements