The Electronic Thermal Conductivity of Graphene

물리천문학부의 김태윤 학생이 제1저자로, 박철환 교수가 교신 저자로, EPFL 의 Nicola Marzari 교수가 공동저자로 참여한 제일원리 계산 연구에서 열전도율이 다른 어떤 물질보다도 높다고 알려진 그래핀의 열전달에 전자가 담당하는 비율이 기존에 알고 있던 것처럼 1% 미만이 아니라 10% 정도 될 수 있고, 크기가 수 마이크론 혹은 그 이하의 샘플에서는 전자의 기여가 상대적으로 중요해짐을 보였다. 그래핀에서 전자가 담당하는 10% 정도의 열전도율은 보통 금속 전체의 열전도율과 크기가 비슷하다. 또한, 샘플에 있는 불순물의 양이 적을수록 Wiedemann-Franz law (전자에 의한 열전도율이 전기전도율과 온도의 곱에 비례한다는 법칙) 에서 많이 어긋남을 알아냈다. 이 연구 결과는 Nano Letters 이번 달 호에 실렸다.

Abstract: Graphene, as a semimetal with the largest known thermal conductivity, is an ideal system to study the interplay between electronic and lattice contributions to thermal transport. While the total electrical and thermal conductivity have been extensively investigated, a detailed first-principles study of its electronic thermal conductivity is still missing. Here, we first characterize the electron–phonon intrinsic contribution to the electronic thermal resistivity of graphene as a function of doping using electronic and phonon dispersions and electron–phonon couplings calculated from first-principles at the level of density-functional theory and many-body perturbation theory (GW). Then, we include extrinsic electron-impurity scattering using low-temperature experimental estimates. Under these conditions, we find that the in-plane electronic thermal conductivity κe of doped graphene is ∼300 W/mK at room temperature, independently of doping. This result is much larger than expected and comparable to the total thermal conductivity of typical metals, contributing ∼10% to the total thermal conductivity of bulk graphene. Notably, in samples whose physical or domain sizes are of the order of few micrometers or smaller, the relative contribution coming from the electronic thermal conductivity is more important than in the bulk limit, because lattice thermal conductivity is much more sensitive to sample or grain size at these scales. Last, when electron-impurity scattering effects are included we find that the electronic thermal conductivity is reduced by 30 to 70%. We also find that the Wiedemann–Franz law is broadly satisfied at low and high temperatures but with the largest deviations of 20–50% around room temperature.