Hall Effect in Bi₂Sr₂CaCu₂O_8+x van der Waals Heterostructures Down to Two Unit Cells

We explore the electronic transport properties of atomically-thin, mechanically exfoliated, optimally doped Bi₂Sr₂CaCu₂O_8+x (BSCCO). We have fabricated superconducting devices with bulk-like superconducting transition behavior down to 1.5 unit cells thickness. In order to avoid degradation of our crystals, the devices are made entirely inside an argon glovebox using a high-resolution stencil mask evaporation method without any exposure to air, resist, solvent, or heat, and with a lateral resolution < 500 nm. The crystals are subsequently protected by hexagonal boron nitride crystal, stacked atop the BSCCO at room temperature in argon. We measure the Hall effect down to two unit cells, which shows a saturation of Hall coefficient at 13T and 75K to the normal state value, and double-sign-reversal in the Hall coefficient (the Hall anomaly) at low fields near Tc. We compare this data to bulk samples. The incorporation of BSCCO into van der Waals heterostructures opens the possibility of a new generation of mesoscopic devices for the study of high temperature superconductivity and their interplay with other van der Waals crystal systems.