Lena ENGSTRÖM : Upper critical field and pairing symmetry of Ising superconductors

Contact: andrej.mesaros@universite-paris-saclay.fr

Le résumé :

    Several conflicting predictions have been made for the symmetry of the pairing in transition metal dichalcogenide (TMD) superconductors. An indication of whether singlet or triplet pairing is present can be given by the upper critical field (Hc), the magnetic field required to fully supress superconductivity. Monolayer NbSe2 and TaS2 have extremely large critical fields, due to a large Ising spin-orbit coupling (SOC) [1], yet their Hc values do not scale with SOC and temperature as expected for other TMDs [2]. 

     I will present our work [3], in which we highlight that the Ising SOC has nodal lines in the Brillouin zone imposed by symmetry. By deriving the susceptibility, we have found that the scaling of the critical field can be traced back to whether the Fermi surface intersects with these nodal lines or not. Reinterpreting existing experimental data, we find that only a predominantly singlet order is consistent with the values and the scaling of measured Hc for several superconducting TMDs. Our analysis extends to multilayer TMDs, for which I will discuss the implications on the pairing symmetry. 

[1] Frigeri, P.A., et al., New J. Phys. 6 115 (2004)

[2] de la Barrera, S.C., Sinko, M.R., Gopalan, D.P. et al., Nat Commun 9, 1427 (2018)

[3] Engström, L., Zullo, L., Cren, T., Mesaros, A., & Simon, P., (in preparation)