laboratoire pierre aigrain
électronique et photonique quantiques
laboratoire pierre aigrain

Séminaire - 15 juin 2009

Jérôme Cayssol<br class='autobr' />CPMOH, Université de Bordeaux, 33405 TALENCE<br class='autobr' />
Quantum transport through normal and superconducting graphene-based transistors

Graphene’s distinctive band structure gives rise to exciting new transport properties and promising applications for carbon-based electronics. In semiconducting nanotubes or graphene nanoribbons, it is well known that Schottky barriers develop at the metallic contacts and may strongly influence the quantum transport. Charge transfer between a metal and a wide graphene sheet also induces potential steps. Recently, the existence of these potential steps was inferred experimentally from the transport properties of a graphene strip with various contact geometries [1]. More direct evidence for these steps comes from optical mapping of the potential landscape across a graphene device [2].
In the first part of my talk, I will discuss how such potential steps modify the conductance and the shot noise of graphene Field Effect Transistors (gFETs) [3]. For ballistic transport between two contacts, successive minima (nodes) of the shot noise are predicted as the two-dimensional electron gas density is increased. In the diffusive regime, we show how the total resistance and Fano Factor of the whole gFET depend upon the contact resistance and Fano factor of each contact.
In the second part, I will describe how a proximity-induced pairing potential barrier modify the non-local transport through a coherent graphene sheet. Owing to the presence of Dirac points, crossed Andreev reflection may dominate the quantum transport in contrast to the usual situation involving massive carriers in metals or semiconductors [4].

[1] B. Huard, N. Stander, J. A. Sulpizio, and D. Goldhaber-Gordon, Phys. Rev. B 78, 121402 (2008).
[2] E.J.H. Lee et al., Nature Nano 3, 486 (2008) ; T. Mueller et al., arXiv:0902.1479
[3] J. Cayssol, B. Huard, and D. Goldhaber-Gordon, Phys. Rev. B 79, 075428 (2009).
[4] J. Cayssol, Phys. Rev. Lett. 100, 147001 (2008).