2007/08/31 by J. H. Chen, C. Jang, M. S. Fuhrer +2 · 1 citation
Physics and Astronomy · #cond-mat.other
paper · pdf · doi:10.1038/nphys935
published as Nature Physics 4, 377 (2008) · 19 pages, 5 figures, Manuscript and figures completely updated
arxiv created 2007/11/09 · arxiv updated 2009/12/01
Since the experimental realization of graphene1, extensive theoretical work has focused on short-range disorder2-5, ''ripples''6, 7, or charged impurities2, 3, 8-13 to explain the conductivity as a function of carrier density sigma_(n)[1,14-18], and its minimum value sigmamin near twice the conductance quantum 4e2/h[14, 15, 19, 20]. Here we vary the density of charged impurities nimp on clean graphene21 by deposition of potassium in ultra high vacuum. At non-zero carrier density, charged impurity scattering produces the ubiquitously observed1, 14-18 linear sigma_(n) with the theoretically-predicted magnitude. The predicted asymmetry11 for attractive vs. repulsive scattering of Dirac fermions is observed. Sigmamin occurs not at the carrier density which neutralizes nimp, but rather the carrier density at which the average impurity potential is zero10. Sigmamin decreases initially with nimp, reaching a minimum near 4e2/h at non-zero nimp, indicating that Sigmamin in present experimental samples does not probe Dirac-point physics14, 15, 19, 20 but rather carrier density inhomogeneity due to the impurity potential3, 9, 10.