The discontinuity in the fields at the interface between the graphene and the substrate leads to residual fields, which also produces components of non-physical DC currents in the sample that remain even without applying external field. In this article we have shown a minimum non-universal conductivity, known as residual conductivity, which is found near the Dirac point that is attributed to the presence of charged impurities near graphene surface and spatial inhomogeneity in the carrier density in agreement to recent data.
