Sign-Reversing Hall Effect in Atomically Thin High-Temperature Bi2.1Sr1.9CaCu2.0O8+δ Superconductors

We developed novel techniques to fabricate atomically thin Bi2.1Sr1.9CaCu2.0O8+delta van der Waals heterostructures down to two unit cells while maintaining a transition temperature T-c close to the bulk, and carry out magnetotransport measurements on these van der Waals devices. We find a double sign change of the Hall resistance E-xy as in the bulk system, spanning both below and above T-c. Further, we observe a drastic enlargement of the region of sign reversal in the temperature-magnetic field phase diagram with decreasing thickness of the device. We obtain quantitative agreement between experimental R-xy (T, B) and the predictions of the vortex dynamics-based description of Hall effect in high-temperature superconductors both above and below T-c.