463 research outputs found
Evidence of Klein tunneling in graphene p-n junctions
Transport through potential barriers in graphene is investigated using a set
of metallic gates capacitively coupled to graphene to modulate the potential
landscape. When a gate-induced potential step is steep enough, disorder becomes
less important and the resistance across the step is in quantitative agreement
with predictions of Klein tunneling of Dirac fermions up to a small correction.
We also perform magnetoresistance measurements at low magnetic fields and
compare them to recent predictions.Comment: Major changes made: 1) Taking into account properly the contribution
of the resistance of monopolar junctions to the odd part of the resistance.
To better present the results we use a fitting parameter for the amplitude of
screening in graphene. 2) Wrong data for the diffusive model in figures 3, 9
and 10 was plotted in former version. 3) Figure 5 moved to EPAP
Contact resistance and shot noise in graphene transistors
Potential steps naturally develop in graphene near metallic contacts. We
investigate the influence of these steps on the transport in graphene Field
Effect Transistors. We give simple expressions to estimate the
voltage-dependent contribution of the contacts to the total resistance and
noise in the diffusive and ballistic regimes.Comment: 6 pages, 4 figures; Figs 3 and 4 completed and appendix adde
Singlet-triplet transition in a single-electron transistor at zero magnetic field
We report sharp peaks in the differential conductance of a single-electron
transistor (SET) at low temperature, for gate voltages at which charge
fluctuations are suppressed. For odd numbers of electrons we observe the
expected Kondo peak at zero bias. For even numbers of electrons we generally
observe Kondo-like features corresponding to excited states. For the latter,
the excitation energy often decreases with gate voltage until a new zero-bias
Kondo peak results. We ascribe this behavior to a singlet-triplet transition in
zero magnetic field driven by the change of shape of the potential that
confines the electrons in the SET.Comment: 4 p., 4 fig., 5 new ref. Rewrote 1st paragr. on p. 4. Revised author
list. More detailed fit results on page 3. A plotting error in the horizontal
axis of Fig. 1b and 3 was corrected, and so were the numbers in the text read
from those fig. Fig. 4 was modified with a better temperature calibration
(changes are a few percent). The inset of this fig. was removed as it is
unnecessary here. Added remarks in the conclusion. Typos are correcte
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