Unconventional superconductivity in graphene on an electron-doped oxide superconductor*

The Bardeen–Cooper–Schrieffer theory of superconductivity describes the condensation of electron pairs with antiparallel spins in a so-called singlet state with s-wave symmetry. Unconventional superconductivity is predicted at certain superconductor interfaces with non-superconducting materials [1], including magnets, materials with strong spin-orbit coupling such as topological insulator and single-layer graphene (SLG). For the case of SLG, the electron pairs are predicted to stabilize to a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) oxide high temperature d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, we have observed evidence for a p-wave triggered superconducting density of states in SLG at temperatures as high as 4.2 K [2]. The nature of the superconducting state is also shown to depend on the underlying facet orientation of the superconductor.

[1] Jacob Linder & Jason WA Robinson, Nature Physics 11, 307–315 (2015).
[2] A Di Bernardo, O Millo, M Barbone, H Alpern, Y Kalcheim, U Sassi, A Ott, D De Fazio, D Yoon, M Amado, AC Ferrari, J Linder, JWA Robinson, Nature Communications 8, 14024 (2017).