Transport and elastic scattering times as probes of the nature of impurity scattering in single and bilayer graphene

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Both transport τtr and elastic scattering times τₑ are experimentally determined from the carrier density dependence of the magnetoconductance of monolayer and bilayer graphene. Both times and their dependences in carrier density are found to be very different in the monolayer and the bilayer. However their ratio τtr/τₑ is found to be of the order of 1.5 in both systems and independent of the carrier density. These measurements give insight on the nature (neutral or charged) and spatial extent of the scattering centers. Comparison with theoretical predictions yields that the main scattering mechanism in our graphene samples could be due to strong scatterers of short range, inducing resonant scattering, a likely candidate being vacancies.