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Tunneling spectroscopy of graphene using planar Pb probes
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View: Figures


Image of FIG. 1.
FIG. 1.

Distinct behaviors of probes made from Pb, Al and Ti/Au on graphene, and of Pb on Au. Time dependence (i.e., oxidation time under ambient conditions) of the probe-on-graphene resistance for different probe materials: (a) Pb, (c) Al, and (d) Ti/Au. (b) Resistance of Pb probes on Au pad as a function of time. Different colors represent data for different probes (for each material, probes were fabricated on several different graphene flakes on multiple substrates). Inset of (a): a scanning electron micrograph (SEM) of a typical device (false-colored for improved contrast). The scale bar is 2 μm.

Image of FIG. 2.
FIG. 2.

Characterization of the Pb tunneling probe at 250 mK. (a) Differential conductance vs. tunnel bias Vb for Pb probes having different resistances at room temperature (oxidized for different times). Conductance for different probes is normalized according to their room temperature (RT) resistances. The more resistive probes show a cleaner gap feature, which originates from superconducting DOS. Oscillations outside the gap edge are shown as fine oscillations inFigure 3(a) . (b) Magnetic field dependence of differential conductance vs. bias voltage. As magnetic field increases, the gap feature gradually disappears, confirming that the gap feature arises from superconductivity.

Image of FIG. 3.
FIG. 3.

Gate and magnetic-field dependence of tunneling spectra. (a) Two-dimensional (2D) map of differential conductance vs. dc bias voltage Vb and backgate voltage Vg, taken on a bilayer sample. The dark horizontal band centered at zero bias comes from the superconducting gap. Arrows point to fine oscillations that disappear with applied magnetic field. White lines are guides to the eye showing broader resonances which persist with magnetic field. (b) Similar 2D map as (a) except with a magnetic field of 8 T perpendicular to the plane of substrate. White lines show broad resonances similar to those in (a). Circles show regions of Coulomb blockade diamonds.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Tunneling spectroscopy of graphene using planar Pb probes