BF-07: Large tunable exchange fields due to purely paramagnetically limited domain wall superconductivity

Local application and precise tunability of large magnetic fields would bear an enticing prospect for generating and detecting Majorana fermions. Such functionality can be readily achieved using Superconductor (S) /Ferromagnet (F) bilayers, where superconductivity is strengthened on top of domain walls due to local lowering of the proximity-induced large effective exchange fields resulting in significant Tc enhancements and possible magnetic switching of this domain wall superconducting (DWS) phase. Using Nb and ferromagnetic insulating (GdN) bilayers and detailed magneto-transport measurements, we demonstrate previously unobserved phenomena of strengthening the DWS phase with shrinkage of cooper pairs. In the thinnest of Nb layers, we estimate in congruence with the theory of domain wall superconductivity that this tunability of proximity-induced exchange fields must be as high as 1.3T with an application of in-plane external fields of few mT.