Quantum scattering time and its implications on scattering sources in graphene

We determine the quantum scattering time tau(q) in six graphene samples with mobility of 4 400 < 17 000 cm(2)/V s over a wide range of carrier density (1.2 < n < 6x10(12)/cm(2)). tau(q) derived from Shubnikov-de Haas oscillation ranges similar to 25-74 fs, corresponding to a single-particle level broadening of 4.5-13 meV. The ratio of the transport to quantum scattering time tau(t)/tau(q) spans 1.5-5.1 in these samples, which can be quantitatively understood combining scattering from short-ranged centers and charged impurities located within 2 nm of the graphene sheet. Our results suggest that charges residing on the SiO2 surface play a dominant role in limiting carrier mobility in current samples.