Abstract

Massless Dirac electron systems such as graphene exhibit a distinct half-integer quantum Hall effect, and in the bipolar transport regime co-propagating edge states along the p–n junction are realized. Additionally, these edge states are uniformly mixed at the junction, which makes it a unique structure to partition electrons in these edge states. Although many experimental works have addressed this issue, the microscopic dynamics of electron partition in this peculiar structure remains unclear. Here we performed shot-noise measurements on the junction in the quantum Hall regime as well as at zero magnetic field. We found that, in sharp contrast with the zero-field case, the shot noise in the quantum Hall regime is finite in the bipolar regime, but is strongly suppressed in the unipolar regime. Our observation is consistent with the theoretical prediction and gives microscopic evidence that the edge states are uniquely mixed along the p–n junction.

Highlights

  • Massless Dirac electron systems such as graphene exhibit a distinct half-integer quantum Hall effect, and in the bipolar transport regime co-propagating edge states along the p–n junction are realized

  • Attributed to the peculiar electron partition caused by uniform mixing of the Quantum Hall (QH) edge states that co-propagate along the p–n junction[9,10], which has been supported by intensive experimental works[11,12,13,14,15,16,17]

  • Theory predicted that the noise is expected to be finite in the bipolar regime, whereas it should disappear in the unipolar regime[10]

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Summary

Introduction

Massless Dirac electron systems such as graphene exhibit a distinct half-integer quantum Hall effect, and in the bipolar transport regime co-propagating edge states along the p–n junction are realized. These edge states are uniformly mixed at the junction, which makes it a unique structure to partition electrons in these edge states. The lateral p–n junctions shown in Fig. 1b are realized in locally gated graphene, and the unique QH edge transport was clarified experimentally[9] and theoretically[10] It was found in the bipolar regime that the QH edge transport at the junction shows a peculiar fractional quantized conductance in the units of conductance quantum e2/h, where h is Planck’s constant[9]. Experiments in this direction, have been lacking so far

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