Van Der Waals-contacted Planar Josephson Junctions*

Recently, many exotic characteristics of graphene and other cleavable two-dimensional (2D) materials have been investigated extensively. Above all, heterosturctures of those 2D materials built by van der Waals (vdW) coupling reveal assorted novel physical properties and atomically flat clean interfaces [1]. Here, we present our preliminary results on the transport characteristics of graphene planar Josephson junctions (JJs), where NbSe₂ was used as a superconducting (SC) electrode material. Graphene–hexagonal-boron-nitride (hBN) bilayer was transferred onto NbSe₂ flakes which were closely pre-arranged to make clean interfaces. Entire graphene and NbSe₂ flakes are encapsulated by a hBN layer to protect the JJ from chemical contamination during the fabrication processes. The JJ thus fabricated by the chemical-free scheme can lead to enhancing the JJ performance. We characterize the Josephson coupling nature of the junctions by examining the temperature and magnetic field dependence of the junction critical current (I_c) and the SC energy gap (Δ), the size of the I_cR_N product (R_N; normal-state junction resistance) in comparison with the 0 K value of Δ/e.