Tuning the effective fine structure constant in graphene: opposing effects of dielectric screening on short- and long-range potential scattering

摘要

We reduce the dimensionless interaction strength in graphene by adding awater overlayer in ultra-high vacuum, thereby increasing dielectric screening.The mobility limited by long-range impurity scattering is increased over 30percent, due to the background dielectric constant enhancement leading toreduced interaction of electrons with charged impurities. However, thecarrier-density-independent conductivity due to short range impurities isdecreased by almost 40 percent, due to reduced screening of the impuritypotential by conduction electrons. The minimum conductivity is nearlyunchanged, due to canceling contributions from the electron/hole puddle densityand long-range impurity mobility. Experimental data are compared withtheoretical predictions with excellent agreement.