Transport in a three-terminal graphene quantum dot in the multi-level regime

TL;DR

This study explores transport properties in a three-terminal graphene quantum dot, measuring conductance matrix elements to understand multi-level interactions and wave function coupling in the Coulomb blockade regime.

Contribution

It provides the first detailed measurement of all conductance matrix elements in a three-terminal graphene quantum dot, revealing level-dependent coupling and spatial wave function insights.

Findings

Different resonance energies depend on the lead pair used for probing.

Localized states do not significantly affect tunneling coupling changes.

Multi-level transport regime allows sensing of individual level coupling strengths.

Abstract

We investigate transport in a three-terminal graphene quantum dot. All nine elements of the conductance matrix have been independently measured. In the Coulomb blockade regime accurate measurements of individual conductance resonances reveal slightly different resonance energies depending on which pair of leads is used for probing. Rapid changes in the tunneling coupling between the leads and the dot due to localized states in the constrictions has been excluded by tuning the difference in resonance energies using in-plane gates which couple preferentially to individual constrictions. The interpretation of the different resonance energies is then based on the presence of a number of levels in the dot with an energy spacing of the order of the measurement temperature. In this multi-level transport regime the three-terminal device offers the opportunity to sense if the individual levels couple with different strengths to the different leads. This in turn gives qualitative insight into the spatial profile of the corresponding quantum dot wave functions.