Electrical control of intervalley scattering via the charge state of defects

We study the intervalley scattering in defected graphene by low-temperature transport measurements. The scattering rate is strongly suppressed when defects are charged. The finding highlights `screening' of the short-range part of a potential by the long-range part. Experiments on calcium adsorbed graphene confirm the role of a long-range Coulomb potential. This effect is applicable to other multivalley systems, provided that the charge state of a defect can be electrically tuned. Our result provides a new means to electrically control valley relaxation and has important implications in valley dynamics in valleytronic materials.