title: Multiple virtual tunneling of Dirac fermions in granular graphene.
abstract: Graphene charge carriers behave as massless Dirac fermions, opening the exciting possibility to observe long-range virtual tunneling of electrons in a solid. In granular metals, electron hops arising from series of virtual transitions are predicted to yield observable currents at low-enough temperatures, but to date experimental evidence is lacking. We report on electron transport in granular graphene films self-assembled by hydrogenation of suspended graphene. While the log-conductance shows a characteristic T(-1/2) temperature dependence, cooling the samples below 10 K drives a triple crossover: a slope break in log-conductance, simultaneous to a substantial increase in magneto-conductance and onset of large mesoscopic conductance fluctuations. These phenomena are signatures of virtual transitions of electrons between distant localized states, and conductance statistics reveal that the high crossover-temperature is due to the Dirac nature of granular graphene charge carriers.
authors.affiliation: 1] Department of Physics, National University of Singapore, Singapore 117542, Singapore [2] NUS Graduate School for Integrative Sciences and Engineering (NGS), Singapore 117456, Singapore [3] Graphene Research Center, National University of Singapore, Singapore 117542, Singapore.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Pachoud
authors.forename: Manu
authors.initials: M
authors.lastname: Jaiswal
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Byung-Hee
authors.initials: BH
authors.lastname: Hong
authors.forename: Jong-Hyun
authors.initials: JH
authors.lastname: Ahn
authors.forename: Kian Ping
authors.initials: KP
authors.lastname: Loh
authors.forename: Barbaros
authors.initials: B
authors.lastname: Ozyilmaz