Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 84: Focus Session: Nanoscopic Superconducting Heterostructures

TT 84.3: Topical Talk

Thursday, March 19, 2015, 10:30–11:00, H 0104

Signature of Magnetic-Dependent Gapless Odd Frequency States at Superconductor / Ferromagnet Interfaces — •Jason Robinson — Department of Materials Science, 27 Charles Babbage Road, Cambridge, CB30FS UK

The theory of superconductivity developed by Bardeen, Cooper, and Schrieffer (BCS) explains the stabilisation of electron pairs into a spin-singlet, even frequency, state by the formation of an energy gap below which the density of states (DoS) is zero. At a superconductor interface with an inhomogeneous ferromagnet, a gapless odd frequency superconducting state is predicted in which the Cooper pairs are in a spin-triplet state. Although indirect evidence for such a state has been obtained, the gap structure and pairing symmetry have not so far been determined. In this talk I will present scanning tunnelling spectroscopy of Nb superconducting films proximity coupled to epitaxial Ho. These measurements reveal pronounced changes to the Nb sub-gap superconducting DoS on driving the Ho through a metamagnetic transition from a helical antiferromagnetic to a homogeneous ferromagnetic state for which a BCS-like gap is recovered. The results verify odd frequency spin-triplet superconductivity at superconductor / inhomogeneous magnet interfaces.