2017/03/22 by Tom Dvir, Dvir, Tom, Freek Massee +11
Physics and Astronomy · #FOS: Physical sciences #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #Superconductivity (cond-mat.supr-con) #Surface and Thin Film Phenomena #Topological Materials and Phenomena
paper · pdf · doi:10.48550/arxiv.1703.07677
openalex publication_date 2017/03/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Device-based tunnel spectroscopy of superconductors was first performed by\nGiaever, whose seminal work provided clear evidence for the spectral gap in the\ndensity of states (DOS) predicted by the Bardeen-Cooper-Schrieffer (BCS)\ntheory. Since then, tunnel-barrier-based heterostructure devices have revealed\nmyriad physical phenomena and found a range of applications. Most of these\ndevices rely on a limited number of oxides, which form high-quality insulating,\nnon-magnetic barriers. These barriers, however, do not grow well on all\nsurfaces. Promising alternatives are van der Waals (vdW) materials, ultrathin\nlayers of which can be precisely positioned on many surfaces; they have been\nshown to form tunnel barriers when engaged with graphene. Here we demonstrate\nthat vdW semiconductors MoS2 and WSe2 deposited on the superconductor\nNbSe2 form high quality tunnel barriers, with transparencies in the\n10-8 range. Our measurements of the NbSe2 DOS at 70mK show a hard\nsuperconducting gap, and a quasiparticle peak structure with clear evidence of\ncontributions from two bands, with intrinsic superconductivity in both bands.\nIn both perpendicular and parallel magnetic fields, we observe a sub-gap DOS\nassociated with vortex bound states. The linear dependence of the zero-bias\nsignal on perpendicular field allows us to confirm the s-wave nature of\nsuperconductivity in NbSe2. As vdW tunnel barriers can be deployed on many\nsolid surfaces, they extend the range of superconducting and other materials\naddressable not only by high resolution tunneling spectroscopy but also\nnon-equilibrium and/or non-local transport.\n