Shot Noise Generated by Graphene p-n Junctions in the Quantum Hall Effect Regime

Norio Kumada1, Francois D. Parmentier3, Hiroki Hibino2,
D. Christian Glattli3, and Preden Roulleau3
1Physical Science Laboratory, 2Materials Science Laboratory, 3CEA Saclay

 In graphene, owing to the linear and gapless band structure, a unique p-n junction, where n-type and p-type regions adjoin each other without a gap in between, is formed. In the quantum Hall effect regime under high magnetic field, counter-circulating electron and hole edge modes mix in the p-n junction [Fig. 1(a)]. In this work, we investigate the mode mixing process by shot noise measurements and suggest that the p-n junction can serve as an electronic beam splitter [1].
 We used graphene grown on SiC. A p-n junction is formed by applying a gate bias to the top gate covering half of the graphene. The current injected to the p-n junction is distributed to electron and hole modes by the mode mixing and then partitioned at the exit of the p-n junction. We measured the shot noise generated by this mode mixing and the subsequent partitioning process. We demonstrate the crucial role of the p-n junction length on the mode mixing process [Fig. 1(b)]. For longer p-n junctions, the shot noise is reduced by the energy relaxation. On the other hand, for p-n junctions with the length shorter than the relaxation length (15 µm), the energy loss to the environment is negligible and the noise is consistent with a quasielastic mode mixing. This suggests that a graphene p-n junction can serve as an electronic beam splitter. Since the beam splitter is an important element of quantum optics, our results encourage using graphene for such applications.

Fig. 1. (a) Counter-circulating electron and hole edge modes in a bipolar graphene quantum Hall effect regime. (b) Shot noise as a function of the source-drain bias for the samples with different p-n junction length.