Probing Triplet Superconductivity by Scanning Tunneling Spectroscopy

Elke Scheer

In this talk we will address the superconducting proximity effect between a superconductor (S) and a normal metal (N) linked by a spin-active interface. With the help of a low-temperature scanning tunneling microscope we study the local density of states of trilayer systems consisting of Al (S), the ferromagnetic insulator EuS, and the noble metal Ag (N). In several recent studies it has been shown that EuS acts as ferromagnetic insulator with well-defined magnetic properties down to very low thickness [1]. We observe pronounced subgap structures that either reveal a zero-bias peak (ZBP) or an additional zero-bias splitting (ZBS) and that can be tuned by a magnetic field. We interpret our findings in the light of recent theories of odd-triplet contributions created by the spin-active interface [2,3]. In particular, we discuss that the ZBS is a hallmark for spin-polarized triplet pairs, able to carry long-ranged supercurrents in to F, while the ZBP is a signature for short-ranged, mixed-spin triplet pairs.

[1] S. Diesch et al., Nature Commun. 9, 5248 (2018)
[2] B. Li et al., Phys. Rev. Lett. 110, 09700 (2013)
[3] A. Cottet et al., Phys. Rev. B 80, 184511 (2009)