Seminar: Proximity induced superconductivity in bilayer graphene-boron nitride van der Waals heterostructures

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Date(s) - 08/12/2014
2 h 00 min - 3 h 00 min

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SEMINAIRE INFORMEL DQMP

Monday December 8,  2014

MaNEP Room – 2.00 p.m.

Proximity induced superconductivity in bilayer graphene-boron nitride van der Waals heterostructures

Romain Danneau (Karlsruhe)

When graphene is placed on an atomically flat substrate its charge carrier mobility dramatically increases and therefore its intrinsic properties can be eventually explored. By pilling up two-dimensional materials one can design artificial heterostructures which are maintained by van der Waals forces. Here we report the study of a high quality bilayer graphene connected by superconducting electrodes and sandwiched between two hexagonal boron nitride layers used as both atomically at substrate and gate dielectric. We show that this system does not remain superconducting around the charge neutrality point which clearly highlight a superconducting to insulator transition at low carrier density. Insulating sates have already been observed in ultraclean suspended bilayer graphene where a spontaneous gap can open due to the high electron-electron interaction in these systems. The presence of anomalous clear low energy features in the differential resistance which cannot be explained by the presence of multiple Andreev reflection is observed at every gate range. The unusual Fraunhofer pattern can be related to the uneven supercurrent density through the device.  We show that both normal state resistance and supercurrent can be tuned by the displacement field created by the top and back gate. Additionally both Ic and IcRn product show a linear dependence in charge carrier density which is expected for ballistic monolayers which again demonstrate the high quality of our device.

 

Réalisation : Sur Mesure concept