Heat conductivity in graphene and related materials: A time-domain modal analysis

Thermal conductivity decomposition in two-dimensional materials: Application to graphene

“…Mode-coupling theory [6] predicts a divergent t −1 scaling of the HCACF for strictly 2D systems and a convergent t for the out-of-plane component, which means that both components eventually saturate and κ for pristine graphene is finite, in agreement with several recent theoretical studies using other approaches [10][11][12][13]34,42], although it is found experimentally that κ is still increasing up to 9 microns [9]. Our results show clearly that the slow convergence of the thermal conductivity is due to the flexural phonons: The convergence of κ out (t) takes a few ns, while κ in (t) converges within a few hundred ps.…”

“…The simulation cell size is about 25 nm × 25 nm (24 000 atoms), which has been shown to be large enough to eliminate finite-size effects [17,34,40] in the Green-Kubo method.…”

“…[40], the running thermal conductivity κ(t) of graphene was computed at 300 K, but only up to a maximum correlation time of t max = 0.5 ns. As pointed out by GillComeau and Lewis [34], this t max is not large enough to observe a complete saturation of the running conductivity. Below, we show that there are actually two distinct time scales governing the time convergence of the running conductivity, and one of them exceeds 0.5 ns.…”

“…The divergence of κ in strained graphene was first predicted [16] to occur for any amount of strain based on firstprinciples lattice dynamics calculations using the single-mode relaxation time approximation, but previous [17,34] and our current MD simulations indicate that the divergence does not occur when 2%. In agreement with Ref.…”

“…There have been intensive efforts in developing MD-based methods for studying spectrally decomposed properties [25][26][27][28][29][30][31][32][33][34][35], but most of them are targeted for general materials. One exception is the method by Gill-Comeau and Lewis [34], where the total thermal conductivity is decomposed into a single-particle component and a collective one, the latter being crucial to materials in which the nonresistive normal (non-umklapp) scattering is important, which is the case for graphene [10,14,15]. Another recent development proposes that heat conduction in 2D materials is due to relaxons, which are wave packets of phonons that arise in the context of the linearized Boltzmann equation [5].…”