Observation of excited states in a graphene quantum dot

TL;DR

This paper reports the detection of excited states in a graphene quantum dot through transport measurements, revealing quantum level fluctuations and Landau level formation under magnetic fields.

Contribution

It introduces direct transport detection of excited states in graphene quantum dots and analyzes magnetic field effects on energy levels.

Findings

Detection of excited states via Coulomb diamonds

Observation of inelastic cotunneling onset

Transition to Landau levels at high magnetic fields

Abstract

We demonstrate that excited states in single-layer graphene quantum dots can be detected via direct transport experiments. Coulomb diamond measurements show distinct features of sequential tunneling through an excited state. Moreover, the onset of inelastic cotunneling in the diamond region could be detected. For low magnetic fields, the positions of the single-particle energy levels fluctuate on the scale of a flux quantum penetrating the dot area. For higher magnetic fields, the transition to the formation of Landau levels is observed. Estimates based on the linear energy-momentum relation of graphene give carrier numbers of the order of 10 for our device.