Spectroscopy of few-layer superconducting NbSe2
Jeudi 16 mai 2019 11:00
- Duree : 1 heure
Lieu : Salle du bâtiment accueil, CEA - 17 rue des Martyrs - Grenoble
Orateur : Marco APRILI (LPS-CNRS Université Paris-Sud, 91400 Orsay, France)
I will address Ising superconductivity in few-layer Transition-Metal-Dichalcogenures (TMD). I will show that van der Waals tunnel barriers, fabricated by exfoliation and tr ansfer of layered semiconductors, sustain stable currents with strong suppression of sub-gap tunneling [1]. This allows us to measure spectra of bulk (20 nm) and ultrathin (3- and 4-layer) NbSe2 devices down to T=70 mK and under applied magnetic field with high energy resolution. These spectra exhibit two distinct superconducting gaps and are analyzed using a two-band model. In the bulk sample, the smaller gap exhibits stronger orbital depairing than the larger one for in-plane magnetic field. This larger depairing results from a higher out-of-plane Fermi velocity to be related to 3D character of electron band associated to this gap. In the few-layer devices, the large gap exhibits negligible depairing, consistent with out-of-plane spin locking due to Ising protection induced by a strong spin–orbit coupling. In the 3-layer device, the large gap persists far beyond the Pauli limit as also expected for Ising superconductors [1]. A very recent spectroscopy experiment in high magnetic field shows that the critical field is actually about 7 larger than the Pauli limit. I will discuss the theoretical scenarios that include Ising spin-orbit and support this result. Finally I will show how spectroscopy in vortex state can be used to elucidate the multi-band aspects of superconductivity in these materials [2].
[1] T. Dvir, F. Massee, L. Attias, M. Khodas, M. Aprili, C.H.L. Quay & H. Steinberg, Nature Commun. 9, 598 (2018)
[2] T. Dvir, M. Aprili, C. H. L. Quay, and H. Steinberg Nano Lett. 18, 12, 7845-7850 (2018)
Contact : johann.coraux@neel.cnrs.fr
Discipline évènement : (Physique)
Entité organisatrice : (INAC/SPSMS)
Nature évènement : (Séminaire)
Site de l'évènement : Site CEA sans badge requis
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