Planar graphene-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>NbSe</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math> Josephson junctions in a parallel magnetic field
Tom Dvir, Ayelet Zalic, Eirik Holm Fyhn, Morten Amundsen, Takashi Taniguchi, Kenji Watanabe, Jacob Linder, Hadar Steinberg
Abstract
Thin transition metal dichalcogenides sustain superconductivity at large in-plane magnetic fields due to Ising spin-orbit protection, which locks their spins in an out-of-plane orientation. Here we use thin $\mathrm{Nb}{\mathrm{Se}}_{2}$ as superconducting electrodes laterally coupled to graphene, making a planar, all van der Waals two-dimensional Josephson junction (2DJJ). We map out the behavior of these novel devices with respect to temperature, gate voltage, and both out-of-plane and in-plane magnetic fields. Notably, the 2DJJs sustain supercurrent up to parallel fields as high as 8.5 T, where the Zeeman energy ${E}_{Z}$ rivals the Thouless energy ${E}_{Th}$, a regime hitherto inaccessible in graphene. As the parallel magnetic field ${H}_{\ensuremath{\parallel}}$ increases, the 2DJJ's critical current is suppressed and in a few cases undergoes suppression and recovery. We explore the behavior in ${H}_{\ensuremath{\parallel}}$ by considering theoretically two effects: a 0-$\ensuremath{\pi}$ transition induced by tuning of the Zeeman energy and the unique effect of ripples in an atomically thin layer which create a small spatially varying perpendicular component of the field. The 2DJJs have potential utility as flexible probes for two-dimensional superconductivity in a variety of materials and introduce high ${H}_{\ensuremath{\parallel}}$ as a newly accessible experimental knob.