Electronic phase coherence and relaxation in graphene field effect transistor

Using the low-field magnetoresistance measurement we have studied the electronic phase coherence of the graphene field effect transistor for different carrier types and densities. The characteristic time scales such as phase coherence time (τφ), intervalley scattering time (τi), and momentum relaxation time have been deduced by weak localization fit to the magnetoresistance. We found that the magnitude of τφ shows similar magnitudes for both types of charge carriers. In the lower density regime including the Dirac point, τφ increases rapidly as the density of carrier increases. However, τi shows a weak dependence of carrier type and density. The momentum relaxation time becomes saturated below 3 K regardless of carrier type and density, which is in contrast to the temperature dependence of τφ.