Controllable quantum devices in bilayer graphene

Quantum dots in graphene have been mostly realized by etching leading to localized states at the disordered edges. [1] It is well known that in bilayer graphene a vertical electric field opens a band gap. [2] Gap-enabled electrostatic confinement has been used with limited success to define quantum devices [3] because of leakage currents thought to occur at the physical sample edges [4]. Here we fabricate electrostatically tunable barriers on bilayer graphene devices with a graphite back gate. We measure pinch-off resistances exceeding GOhms and observe quantized conductance plateaus in one-dimensional constrictions. [5] With suitable gate geometries, few-carrier hole and electron quantum dots can be electrostatically defined. We control the occupation of quantum dots with single holes and electrons. Four-fold level bunching is observed in Coulomb blockade spectroscopy which is related to valley and spin states. The magnetic field dependenct conductance allows us to investigate orbital and spin/valley effects.
[1] For a review see Bischoff et al., Applied Physics Reviews 2, 031301 (2015)
[2] Oostinga et al., Nat. Materials 7, 151 (2007)
[3] Allen et al., Nat. Comm. 3, 934 (2012)
[4] Zhu et al., Nat. Comm. 8, 14552 (2017)
[6] Overweg et al., arXiv:1707.09282, arXiv:1709.00870