4H-SiC substrate preparation - graphitization annealing Polished SiC substrate SiC steps Graphitized substrate

Patterning

e-beam lithography Hall bar FET Quantum Interference loop

Epitaxial graphene grown on SiC Highly ordered and well defined material Transport layer is protected Graphene properties : Dirac - chiral electrons Anomalous Berry’s phase Weak anti-localization Landau level spectrum Long electronic phase coherence length Ballistic properties, high mobility Anomalous transport : no quantum Hall effect periodic and fractal-like spectrum for high mobility samples AFM

Magneto-transport of a wide Hall bar (EG on Si-face) Shubnikov - de Haas magnetoresistance maxima Rxx (Ω/sq) Rxy (Ω) 0.3-4K Field(T) 400µm

Magneto-transport and Landau levels Dirac particles: linear E(k) Magnetic field Energy 3 EF 2 3 4 1 -1 -2 -3 1/Bn (T-1) Landau index (n) Energy Magnetic field Normal electrons: quadratic E(k) EF Landau plot : Slope gives carrier density ns= 1.3 1012cm-2 Intercept at n=0 indicates anomalous Berry’s phase see K. Novoselov et al. Nature 438, 197 (2005); Y. Zhang et al. Nature 438, 201 (2005) W.de Heer et al., cond-mat /0704.0285

Temperature dependence of the SdH peaks Landau levels thermally populated Lifshitz-Kosevich equation : A(T)/Ao= u/sinh(u) where u=2π2kBT/∆E(B) Energy Magnetic field DE/kB(K) 1 ∆E(B)= vF=0.75 106m/s T e m p e r a t u r e V. Gusynin, Phys. Rev. B 71,125124 (2005)

Transport is graphene-like surprising 3 layers Low mobility µ=1100 cm2/Vs Disordered as seen in STM (graphene on Si-face) Phase coherence length lf(T=4K)~100nm In agreement with STM-STS Scattering by defects for graphene on the Si-face G. Rutter, J. Stroscio et al., Science to be published P. Mallet, J.-Y.Veuillen et al. cond-mat/0702406

Interface charging Interface layer dominates transport Neutral layers seen in Landau level IR spectroscopy Sadowski PRL97, 266405 (2006) 5 nm TEM -cross section Daniel Ugarte, LNLS, Brasil n~1012/cm2 n~1010/cm2 E Graphene layers SiC Workfunction graphite-Workfunction SiC V ~0.3 eV Built-in electric field E= V/L L is of order of screening length. Hence interface layer is charged ns~ E/0 ~1012/cm2 (Note: n~1010/cm2 for neutral graphite) See also photoemission ARPES - A. Botswick et al. Nature Physics 3, 36 (2007) E. Rolling et al. cond-mat/0512226 (2005) - J. Phys Chem Solid 67, 2172 (2006) T. Seyller et al. , Surface Science 600, 3906 (2006).