School of Physics Hard Condensed Matter Seminar: Prof. Gleb Finkelstein, Duke University

One of the promising routes towards creating novel topological states and excitations is to combine superconductivity with quantum Hall (QH) effect. However, signatures of superconductivity in the QH regime remain scarce, and a superconducting current through a QH weak link has until recently eluded experimental observation. Here, we explore high mobility graphene/boron nitride heterostructures contacted by type II superconducting electrodes that could withstand magnetic fields of a few Tesla.

At low magnetic fields, our devices demonstrate the Fraunhoffer pattern and Fabri-Perot oscillations, confirming their uniformity and ballisticity. At fields of 1-2 Tesla, when Landau quantization is fully developed, regions of superconductivity can be observed on top of the conventional QH fan diagram. The measured supercurrent is very small, on a few nA scale, and periodic in magnetic field.

Additional measurements on side- and top-gated samples shed light on the alternative mechanisms that mediate supercurrent along the QH edge states. Finally, we demonstrate the evidence of the “Andreev edge states” – single particle electron-hole hybrid states propagating along the QH-superconductor boundary.