Current Applied Physics, Vol.19, No.3, 251-255, 2019
Planar graphene Josephson coupling via van der Waals superconducting contacts
We report on the fabrication and transport characteristics of van der Waals (vdW)-contacted planar Josephson junctions. In a device, two pieces of cleaved 2H-NbSe2 superconducting flakes and a monolayer graphene sheet serve as the superconducting electrodes and the normal-conducting spacer, respectively. A stack of NbSe2 - graphene-hexagonal-boron-nitride (hBN) heterostructure with clean and flat interfaces was prepared by a dry transfer technique. The outermost hBN layer protected the NbSe2 - graphene - NbSe2 Josephson junction from chemical contamination during the fabrication processes. The Josephson coupling was confirmed by a periodic modulation of the junction critical current I in a perpendicular magnetic field. The temperature dependence of I showed long and diffusive Josephson coupling characteristics. The temperature dependence of the superconducting gap, obtained from the multiple Andreev reflection features, followed the Bardeen - Cooper - Schrieffer (BCS) prediction.