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

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 a...

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Bibliographic Details
Published in:Nature communications 2018-02, Vol.9 (1), p.1-6, Article 598
Main Authors: Dvir, T., Massee, F., Attias, L., Khodas, M., Aprili, M., Quay, C. H. L., Steinberg, H.
Format: Article
Language:English
Subjects:
639/766/119/1003
639/766/119/995
639/925/357/1018
Condensed Matter
Critical temperature
Electronics industry
Humanities and Social Sciences
Ising model
Magnetic fields
Materials selection
Mesoscopic Systems and Quantum Hall Effect
multidisciplinary
Oxides
Physics
Science
Science (multidisciplinary)
Spectroscopy
Spectrum analysis
Strongly Correlated Electrons
Superconductivity
Tunnel junctions
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Summary: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) NbSe 2 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. Ideal tunnel junctions require high-quality, defect-free insulating barriers. Here, the authors demonstrate that van der Waals tunnel barriers atop bulk and ultrathin superconducting NbSe 2 sustain a stable tunneling current and allow mapping of the spectral evolution of layered superconductors.
ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-018-03000-w