In conventional superconductors electrons are bound in singlet Cooper pairs, i.e. with opposite spin. More recently experiments on superconductor-ferromagnet-systems have shown Cooper pairs tunneling through ferromagnetic layers, indicating Cooper pairs of equal spin, thus corresponding to a long-range triplet proximity effect . Most experimental evidence for triplet superconductivity comes from observations of the thickness dependence of the Josephson current through a ferromagnetic barrier, and there now is an increasing amount of direct spectroscopic evidence (e.g. our results measured on niobium/holmium multilayers ) to test the existing theoretical models .
This project aims to analyze the DOS of thin films of the ferromagnetic insulator europium sulfide on superconducting aluminum or vice versa, using a scanning tunneling microscope in spectroscopy mode at 280 mK and in varying magnetic fields. We observe significant broadening of the superconducting energy gap and a variety of sub-gap structures induced by the presence of the ferromagnet. We interpret our findings based on the diffusive theory [4,5] and a more advanced circuit theory model .
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Contributors: Simon Diesch, Peter Machon, Wolfgang Belzig
Former contributors: Michael Wolz
External cooperations: Christoph Sürgers, Detlef Beckman, Angelo Di Bernardo, Jason Robinson
Fundings: Landesgraduiertenförderungsgesetz (LGFG), The Leverhulme Trust
Period: since 2014