Elsevier, Physics Letters A, 9(377), p. 721-726
DOI: 10.1016/j.physleta.2013.01.013
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This work reports on the phonon energy inversion in graphene nanoribbons: after initial localized thermal excitation, the energy of initial cold phonons (flexural mode: FM) becomes higher than that of local hot phonons (longitudinal and transverse modes: LM/TM). Such energy inversion holds for about 50 picoseconds. Two physical factors combine together to give rise of this phenomenon: one is the much faster heat conduction by FM phonons than that by LM/TM phonons, and the other factor is the strongly temperature-dependent energy exchange rate between FM and LM/TM phonons: 3.7×1010 s−13.7×1010 s−1 at 84 K to 20.3×1010 s−120.3×1010 s−1 at around 510 K.