Figure 1

Conductivity evolution after Ir deposition.

(a) The conductivity σ versus gate voltage V_g for pristine graphene and at four different Ir coverages taken at 7 K. Here 1 ML = 1.56 × 10¹⁵ cm⁻² is defined from the atomic density of the Ir(111) surface. (b) Inverse of electron mobility 1/μ_e and hole mobility 1/μ_h versus Ir coverage. Lines are linear fits to all data points. Inset: The ratio of μ_e to μ_h versus Ir coverage. The blue line corresponds to the electron-hole asymmetry observed for potassium in ref. 3. (c) The shift of gate voltage of minimum conductivity –ΔV_g,min as a function of 1/μ_e, which is proportional to the impurity concentration. All –ΔV_g,min values are offset by 2 V to account for initial disorder. (d) The minimum conductivity σ_min as a function of 1/μ_e. Lines in (c,d) correspond to the theory in ref. 3.