Phonon Engineering of the Specific Heat of Twisted Bilayer Graphene: The Role of the Out-of-Plane Phonon Modes

Abstract

We investigated theoretically the specific heat of graphene, bilayer graphene and twisted bilayer graphene taking into account the exact phonon dispersion and density of states for each polarization branch. It is shown that contrary to a conventional believe the dispersion of the out-of-plane acoustic phonons - referred to as ZA phonons - deviates strongly from a parabolic law starting from the frequencies as low as ~100 1/cm. This leads to the frequency-dependent ZA phonon density of states and the breakdown of the linear dependence of the specific heat on temperature T. We established that ZA phonons determine the specific heat for T<200 K while contributions from both in-plane and out-of-plane acoustic phonons are dominant for 200 K < T < 500 K. In the high-temperature limit, T>1000 K, the optical and acoustic phonons contribute approximately equally to the specific heat. The Debye temperature for graphene and twisted bilayer graphene was calculated to be around ~1861 - 1864 K. Our results suggest that the thermodynamic properties of materials such as bilayer graphene can be controlled at the atomic scale by rotation of the sp2-carbon planes.

25 pages, 5 figures

References in corpus (6)

• Continuum Model of the Twisted Bilayer
• The phonon dispersion of graphite by inelastic x-ray scattering
• Anomalous Size Dependence of the Thermal Conductivity of Graphene Ribbons
• Phonon dispersions and vibrational properties of monolayer, bilayer, and trilayer graphene
• Effect of Grain Boundaries on Thermal Transport in Graphene
• Specific Heat of Twisted Bilayer Graphene

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• Lifshitz transition and thermoelectric properties of bilayer graphene
• Atomistic Engineering of Phonons in Functional Oxide Heterostructures
• Magneto-oscillations on specific heat of graphene monolayer
• Small Angle and Non-Monotonic Behavior of the Thermal Conductivity in Twisted Bilayer Graphene
• Review of Graphene-based Thermal Polymer Nanocomposites: Current State of the Art and Future Prospects