Achievement 2

"Finite-bias spectroscopy of a three-terminal graphene quantum dot in the multilevel regime"


Graphene quantum dots are considered as promising candidates for solid state spin qubits due to their predicted long spin lifetimes. In order to initialize, manipulate, and read out such qubits, access to the discrete energy levels of the quantum dots are needed. A convenient and widely used method to investigate the electronic structure of quantum dots is measuring lines of enhanced conductance parallel to the edges of the Coulomb diamonds. These are due to transport through excited states, but can be accompanied by other lines of which the origin is not yet completely understood. Possible origins that have been suggested are modulation of the tunnel coupling due to resonances in the constrictions and phonon-mediated transport.

We have performed finite-bias spectroscopy measurements of a three-terminal graphene quantum dot in the multi-level regime, which nonetheless revealed a rich spectrum of lines of enhanced conductance outside the Coulomb diamonds. We could discuss the possible origins of these lines by exploiting the additional information about transport through the individual leads obtained from the special three-terminal configuration of this dot.


Figure: Differential conductance (dI1/dV2) through lead 1 as a function of bias voltage applied to lead 2 and back gate voltage.
Regions of negative differential conductance are marked in black.

Reference: "Finite-bias spectroscopy of a three-terminal graphene quantum dot in the multilevel regime”,
A. Jacobsen, P. Simonet, K. Ensslin and T. Ihn, arxiv:1405.1393, Phys. Rev. B 89, 165413 (2014).



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