Specific heat in graphene: role of the out-of-plane phonons
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NIKA, Denis. Specific heat in graphene: role of the out-of-plane phonons. In: Integrare prin cercetare şi inovare.: Ştiinţe ale naturii şi exacte, 10-11 noiembrie 2015, Chișinău. Chisinau, Republica Moldova: Universitatea de Stat din Moldova, 2015, R, SNE, pp. 143-144.
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Integrare prin cercetare şi inovare.
R, SNE, 2015
Conferința "Integrare prin cercetare şi inovare"
Chișinău, Moldova, 10-11 noiembrie 2015

Specific heat in graphene: role of the out-of-plane phonons


Pag. 143-144

Nika Denis
 
Moldova State University
 
Disponibil în IBN: 11 noiembrie 2019


Rezumat

The discovery of the unusually high thermal conductivity of suspended graphene and few-layer graphene (FLG) [1-4] resulted in a surge of interest to thermal properties of two-dimensional materials [4-7]. In this talk I review recent theoretical results on the phonon density of states and specific heat of single-layer graphene (SLG), bilayer graphene (BLG) and twisted bilayer graphene (T-BLG) [5]. It is shown that 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 cm-1 . 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 [5]. It is 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. Temperature-dependence of the heat capacity in SLG, BLG and T-BLG can be approximated by a function aT + bT2 at T<350 K, where parameters a and b were determined by fitting the accurate ( ) Vc T curves. The presented results confirm that the accurate phonon density of states is required for both qualitative and quantitative description of the specific heat of SLG, BLG and T-BLG.