Ballistic interferences in suspended graphene

TL;DR

This paper demonstrates the fabrication of suspended graphene p-n junctions that exhibit ballistic electron interference patterns, advancing the development of electron optics devices in graphene through electrostatic gating and quantum interference control.

Contribution

It reports the creation of fully suspended graphene p-n junctions with tunable resonant cavities, enabling complex Fabry-Perot interference patterns and enhanced electron collimation.

Findings

Observation of quantum interference over distances exceeding 1 micron.

Enhanced interference visibility due to Klein collimation at p-n interfaces.

Potential for developing complex gate-controlled ballistic graphene devices.

Abstract

Graphene is a 2-dimensional (2D) carbon allotrope with the atoms arranged in a honeycomb lattice. The low-energy electronic excitations in this 2D crystal are described by massless Dirac fermions that have a linear dispersion relation similar to photons. Taking advantage of this optics-like electron dynamics, generic optical elements like lenses, beam splitters and wave guides have been proposed for electrons in engineered ballistic graphene. Tuning of these elements relies on the ability to adjust the carrier concentration in defined areas, including the possibility to create bipolar regions of opposite charge (p-n regions). However, the combination of ballistic transport and complex electrostatic gating remains challenging. Here, we report on the fabrication and characterization of fully suspended graphene p-n junctions. By local electro-static gating, resonant cavities can be defined, leading to complex Fabry-Perot interference patterns in the unipolar and the bipolar regime. The amplitude of the observed conductance oscillations accounts for quantum interference of electrons that propagate ballistically over long distances exceeding 1 micron. We also demonstrate that the visibility of the interference pattern is enhanced by Klein collimation at the p-n interface. This finding paves the way to more complex gate-controlled ballistic graphene devices and brings electron optics in graphene closer to reality.