Abstract
Graphene offers a unique system to investigate transport of Dirac Fermions at p–n junctions. In a magnetic field, combination of quantum Hall physics and the characteristic transport across p–n junctions leads to a fractionally quantized conductance associated with the mixing of electron-like and hole-like modes and their subsequent partitioning. The mixing and partitioning suggest that a p–n junction could be used as an electronic beam splitter. Here we report the shot noise study of the mode-mixing process and demonstrate the crucial role of the p–n junction length. For short p–n junctions, the amplitude of the noise is consistent with an electronic beam-splitter behaviour, whereas, for longer p–n junctions, it is reduced by the energy relaxation. Remarkably, the relaxation length is much larger than typical size of mesoscopic devices, encouraging using graphene for electron quantum optics and quantum information processing.
Highlights
Graphene offers a unique system to investigate transport of Dirac Fermions at p–n junctions
In the quantum Hall (QH) effect regime under high magnetic field B, the conductance across a p–n junction (PNJ) shows plateaus at GPNJ 1⁄4 G0|n1||n2|/(|n1| þ |n2|), where G0 1⁄4 e2/h is the conductance quantum (h is Planck’s constant), n1 1⁄4 2, 6, 10, y and n2 1⁄4 À 2, À 6, À 10, y are the Landau level filling factor in the n and p regions, respectively[7,8,9]. This conductance quantization in bipolar QH states has been explained by the mixing of counter-circulating electron and hole edge modes[10,11]: the current injected to the PNJ is distributed to electron and hole modes in the PNJ by the mode mixing with the ratio depending on the number of each modes, on n1 and n2, and partitioned at the exit of the PNJ (Fig. 1b)
Shot noise measurements can provide insight into the mode-mixing mechanism (Supplementary Figs 1 and 4): when the electron and hole modes biased by Vsd are mixed, the energy distribution in the PNJ fPNJ(E) becomes out-of-equilibrium and the subsequent partitioning of the modes gives rise to the shot noise
Summary
Graphene offers a unique system to investigate transport of Dirac Fermions at p–n junctions. In the quantum Hall (QH) effect regime under high magnetic field B, the conductance across a PNJ shows plateaus at GPNJ 1⁄4 G0|n1||n2|/(|n1| þ |n2|), where G0 1⁄4 e2/h is the conductance quantum (h is Planck’s constant), n1 1⁄4 2, 6, 10, y and n2 1⁄4 À 2, À 6, À 10, y are the Landau level filling factor in the n and p regions, respectively[7,8,9] This conductance quantization in bipolar QH states has been explained by the mixing of counter-circulating electron and hole edge modes[10,11]: the current injected to the PNJ is distributed to electron and hole modes in the PNJ by the mode mixing with the ratio depending on the number of each modes, on n1 and n2, and partitioned at the exit of the PNJ (Fig. 1b). Inelastic processes between modes in the PNJ may occur, causing fPNJ(E) to relax towards a Fermi distribution with a finite temperature Teff(Vsd) given by the balance between the Joule power dissipated in the PNJ and the heat flowing along the outgoing electronic channels[10,19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
