Decoherence reduces thermal energy loss in graphene quantum dots

Intraband splitting energies in graphene quantum dots are on the order of the fundamental phonon energies, creating a single-phonon relaxation pathway. Yet, charge carrier thermalization is slow. Our time-domain, ab initio computations demonstrate that the slow rate of electronic relaxation is due to quantum decoherence. The relaxation through the discrete states occurs on a 30 ps timescale. Electron-hole recombination takes place within 660 ps, two orders of magnitude slower than a coherent mechanism. Disorder introduced by structural variations around the edge expedites coherence loss, increasing the lifetimes of excited charge carriers in graphene quantum dots. (C) 2013 AIP Publishing LLC.