Spectroscopy of bulk and few-layer superconducting NbSe2 with van der Waals tunnel junctions.

ABSTRACT: Tunnel junctions, an established platform for high resolution spectroscopy of superconductors, require defect-free insulating barriers; however, oxides, the most common barrier, can only grow on a limited selection of materials. We show that van der Waals tunnel barriers, fabricated by exfoliation and transfer of layered semiconductors, sustain stable currents with strong suppression of sub-gap tunneling. This allows us to measure the spectra of bulk (20?nm) and ultrathin (3- and 4-layer) NbSe2 devices at 70?mK. These exhibit two distinct superconducting gaps, the larger of which decreases monotonically with thickness and critical temperature. The spectra are analyzed using a two-band model incorporating depairing. In the bulk, the smaller gap exhibits strong depairing in in-plane magnetic fields, consistent with high out-of-plane Fermi velocity. In the few-layer devices, the large gap exhibits negligible depairing, consistent with out-of-plane spin locking due to Ising spin-orbit coupling. In the 3-layer device, the large gap persists beyond the Pauli limit.

SUBMITTER: Dvir T 

PROVIDER: S-EPMC5807409 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature