Tunneling Spectroscopy of Layered Superconductors

Hadar Steinberg
Racah Institute of Physics, Hebrew University of Jerusalem, Israel
Thursday, May 13, 2021
10:00 am
Zoom Seminar
Materials such as NbSe2 are superconductors which can be exfoliated down to the single layer limit, while retaining superconducting properties. At this limit a strong spin orbit term protects superconductivity by keeping the spins at an out of plane orientation. Theory developed in recent years [1] suggest that a strong in-plane field tilts the spins, inducing an exotic equal-spin-pairing state in NbSe2 and similar materials. Detecting such physics experimentally, however, is a major challenge, requiring a stable tunneling experiment for probing the excitation spectra under high fields. In my talk I will introduce our method for creating tunnel junctions based on van der Waals (vdW) materials [2, 3]. The vdW junctions are characterized by hard gap tunneling, allowing for tracking the spectra at high fields. Our spectra, measured up to in-plane fields of 33 T, become stable at fields above 25 T, in agreement with a theoretical model suggesting the onset of an equal-spin triplet order [4]. I will also show how defects in the barriers can give rise to Andreev states [5], and can utilized as energy probes [6]. Finally, I will show new data demonstrating the use of NbSe2 as a source-drain electrode in a graphene-based Josephson device, which can sustain high in-plane fields [7].


1. Möckli, D. and M. Khodas, Robust parity-mixed superconductivity in disordered monolayer transition metal dichalcogenides. Physical Review B, 2018. 98(14): p. 144518.
2. Dvir, T., et al., Spectroscopy of bulk and few-layer superconducting NbSe2 with van der Waals tunnel junctions. Nature Communications, 2018. 9(1): p. 598.
3. Dvir, T., et al., Tunneling into the Vortex State of NbSe2 with van der Waals Junctions. Nano Letters, 2018. 18(12): p. 7845-7850.
4. Kuzmanović, M., et al., Tunneling spectroscopy of few-monolayer NbSe2 in high magnetic field: Ising protection and triplet superconductivity. arXiv: 2104.00328, 2021.
5. Dvir, T., et al., Zeeman Tunability of Andreev Bound States in van der Waals Tunnel Barriers. Physical Review Letters, 2019. 123(21): p. 217003.
6. Keren, I., et al., Quantum-dot assisted spectroscopy of degeneracy-lifted Landau levels in graphene. Nature Communications, 2020. 11(1): p. 3408.
7. Dvir, T., et al., Planar graphene-NbSe2 Josephson junctions in a parallel magnetic field. Physical Review B, 2021. 103(11): p. 115401.
Javier Sanchez-Yamagishi