Massless Dirac Fermions Trapping in a Quasi-one-dimensional npn Junction of a Continuous Graphene Monolayer

TL;DR

This paper demonstrates that massless Dirac fermions in graphene can be trapped in a quasi-one-dimensional npn junction, forming quasi-bound states, challenging the traditional view of their unimpeded transmission due to Klein tunneling.

Contribution

The study provides experimental and theoretical evidence of trapping Dirac fermions in graphene using a quasi-1D npn junction, revealing new confinement phenomena.

Findings

Observation of quasi-bound states in graphene npn junctions

Visualization of quantum interference patterns via STM

Confirmation of Dirac fermion trapping contrary to Klein tunneling expectations

Abstract

Massless Dirac fermions in graphene provide unprecedented opportunities to realize the Klein paradox, which is one of the most exotic and striking properties of relativistic particles. In the seminal theoretical work [Katsnelson et al., Nat. Phys. 2 620 (2006)], it was predicted that the massless Dirac fermions can pass through one-dimensional (1D) potential barriers unimpededly at normal incidence. Such a result seems to preclude confinement of the massless Dirac fermions in graphene by using 1D potential barriers. Here, we demonstrate, both experimentally and theoretically, that massless Dirac fermions can be trapped in quasi-1D npn junction of a continuous graphene monolayer. Because of highly anisotropic transmission of the massless Dirac fermions at n-p junction boundaries (the so-called Klein tunneling in graphene), charge carries incident at large oblique angles will be reflected from one edge of the junction with high probability and continue to bounce from the opposite edge. Consequently, these electrons are trapped for a finite time to form quasi-bound states in the quasi-1D npn junction. The quasi-bound states seen as pronounced resonances are probed and the quantum interference patterns arising from these states are directly visualized in our scanning tunneling microscope measurements.