The quantum scattering time and its implications on scattering sources in graphene

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We determine the quantum scattering time tauq in six graphene samples with mobility of 4,400 < mu < 17,000 cm²/Vs over a wide range of carrier density (1.2 < n < 6x10¹²/cm²). tauq derived from Shubnikov-de Haas oscillations ranges 25-74 fs, corresponding to a single-particle level broadening of 4.5-13 meV. The ratio of the transport to quantum scattering time tauₜ/tauq 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.