Quantum interference and Klein tunneling in graphene heterojunctions

TL;DR

This paper reports the experimental observation of quantum conductance oscillations and Klein tunneling in narrow graphene heterostructures, demonstrating electron collimation and phase coherence in unconfined two-dimensional systems.

Contribution

It provides the first direct experimental evidence of Klein tunneling and electron collimation effects in graphene heterojunctions with electrostatically defined barriers.

Findings

Observation of conductance oscillations in graphene heterostructures

Confirmation of Klein tunneling through phase shift analysis

Electrostatically created p-n junctions act as collimators

Abstract

The observation of quantum conductance oscillations in mesoscopic systems has traditionally required the confinement of the carriers to a phase space of reduced dimensionality. While electron optics such as lensing and focusing have been demonstrated experimentally, building a collimated electron interferometer in two unconfined dimensions has remained a challenge due to the difficulty of creating electrostatic barriers that are sharp on the order of the electron wavelength. Here, we report the observation of conductance oscillations in extremely narrow graphene heterostructures where a resonant cavity is formed between two electrostatically created bipolar junctions. Analysis of the oscillations confirms that p-n junctions have a collimating effect on ballistically transmitted carriers. The phase shift observed in the conductance fringes at low magnetic fields is a signature of the perfect transmission of carriers normally incident on the junctions and thus constitutes a direct experimental observation of ``Klein Tunneling.''