Observation of angle-dependent transmission of Dirac electrons in graphene hetero junctions

TL;DR

This study directly measures how the transmission of Dirac electrons in graphene varies with angle, confirming theoretical predictions of angle-dependent Klein tunneling and interference effects in ballistic graphene heterojunctions.

Contribution

It provides the first direct experimental observation of angle-dependent transmission in graphene heterojunctions, validating models of chiral electron interference and Klein tunneling.

Findings

Large oscillations in transmission at 45° angle

Confirmation of interference effects in ballistic graphene

Observation of angle-dependent Klein tunneling signatures

Abstract

The relativistic nature of charge carriers in graphene is expected to lead to an angle- dependent transmission through a potential barrier, where Klein tunneling involves annihilation of an electron and a hole at the edges of the barrier. The signatures of Klein tunneling have been observed in gated graphene devices, but the angle dependence of the transmission probability has not been directly observed. Here we show measurements of the angle-dependent transmission through quasi-ballistic graphene heterojunctions with straight and angled leads, in which the barrier height is controlled by a shared gate electrode. Using a balanced differential measurement technique, we isolate the angle-dependent contribution to the resistance from other angle-insensitive, gate-dependent and device-dependent effects. We find large oscillations in the transmission as a function of the barrier height in the case of Klein tunneling at a 45 deg angle, as compared to normal incidence. Our results are consistent with the model that predicts oscillations of the transmission probability due to interference of chiral carriers in a ballistic barrier. The observed angle dependence is the key element behind focusing of electrons and the realization of a Veselago lens in graphene.