Abstract
We explore the contributions to the electrical resistance of monolayer and bilayer graphene, revealing transitions between different regimes of charge carrier scattering. In monolayer graphene at low densities, a nonmonotonic variation of the resistance is observed as a function of temperature. Such behaviour is consistent with the influence of scattering from screened Coulomb impurities. At higher densities, the resistance instead varies in a manner consistent with the influence of scattering from acoustic and optical phonons. The crossover from phonon-, to charged-impurity, limited conduction occurs once the concentration of gate-induced carriers is reduced below that of the residual carriers. In bilayer graphene, the resistance exhibits a monotonic decrease with increasing temperature for all densities, with the importance of short-range impurity scattering resulting in a “universal” density-independent (scaled) conductivity at high densities. At lower densities, the conductivity deviates from this universal curve, pointing to the importance of thermal activation of carriers out of charge puddles. These various assignments, in both systems, are made possible by an approach of “differential-conductance mapping”, which allows us to suppress quantum corrections to reveal the underlying mechanisms governing the resistivity.
Highlights
We explore the contributions to the electrical resistance of monolayer and bilayer graphene, revealing transitions between different regimes of charge carrier scattering
The weak temperature dependence observed in the monolayer indicates that the dominant source of resistivity in this material, at all densities, is long-range Coulomb disorder
Having described how the quantum corrections may be suppressed in our studies, we focus in more detail on the resistance variations exhibited by the monolayer (Fig. 3) and bilayer (Fig. 4) devices
Summary
We explore the contributions to the electrical resistance of monolayer and bilayer graphene, revealing transitions between different regimes of charge carrier scattering. On the other hand, is usually attributed to the presence of long-range charged impurities in the dielectric substrate[13,14,15,16,17,18,19], and of short-range neutral defects in the graphene itself[15, 16, 18, 20, 22] These mechanisms may combine to yield complicated variations of the resistance as a function of both temperature (T) and carrier density (n & p for electrons and holes, respectively). We study the resistance of graphene/SiO2 transistors over a wide range of temperature (3–300 K), and for densities spanning the electron and hole branches of the Dirac cone Due to their different energy dispersions, the importance of Coulomb and short-range impurities is expected to be very different in monolayer and bilayer graphene[22]. Our findings in both the monolayer and bilayer systems are in good agreement with the theories[1, 20, 22, 23, 45] proposed by Das Sarma and his colleagues
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