Exploiting Aharonov-Bohm oscillations to probe Klein tunneling in tunable pn-junctions in graphene

TL;DR

This paper demonstrates how Aharonov-Bohm oscillations in a graphene ring can be used to probe Klein tunneling and the tunability of pn-junction transparency, revealing a wide range of gate-controlled junction behaviors.

Contribution

It introduces a method to measure Klein tunneling efficiency in graphene using interference patterns in a tunable Aharonov-Bohm ring.

Findings

Gate-controlled pn-junction transparency from 35% to 100%.

Interference patterns reveal Klein tunneling efficiency.

Results agree with semiclassical models.

Abstract

One of the unique features of graphene is that the Fermi wavelength of its charge carriers can be tuned electrostatically over a wide range. This allows in principle to tune the transparency of a pn-junction electrostatically, as this depends on the ratio between the physical extension of the junction and the electron wavelength, i.e. on the effective width of the junction itself. However, this simple idea - which would allow to switch smoothly between a Veselago lens and a Klein-collimator - has proved to be difficult to demonstrate experimentally because of the limited amount of independently-tunable parameters available in most setups. In this work, we present transport measurements in a quasi-ballistic Aharonov-Bohm graphene ring with gate tunable pn-junctions in one arm, and show that the interference patterns provide unambiguous information on the Klein tunneling efficiency and on the junctions effective width. We find a gate-controlled transparency of the pn-junctions ranging from 35-100%. Our results are in excellent agreement with a semiclassical description.