Fabrication of Josephson junctions with nano-injectors and investigation of fractional flux quanta.

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Artificial phase discontinuities allow to create Josephson vortices carrying a magnetic flux, whichis an arbitrary fraction of a single flux quantum. Few experiments with these fractional Josephsonvortices were already reported by our and other groups. However, vortices created by artificialphase discontinuities are rather large in size and investigation of multi-vortex systems such asvortex molecules or 1D crystals was not possible up to now. A limiting factor is the width ofthe current injectors used to produce a phase discontinuity and the critical current density jc ofthe Josephson junction. By using e-beam lithography we are going to fabricate nano-injectors(ideally two injectors of the width ∼ 100 nm with a gap of ∼ 200 nm in between), and reduce theJosephson junction width down to ∼ 300 nm. This will allow to safely increase the jc to a fewkA/cm2 to decrease the vortex size ∝ 1/√jc. Using the new technology we will investigate multivortexmolecules and 1D vortex crystals in the clasical domain at temperatures T ∼ 0.3 . . . 6K.The successful implementation of this project will push forward the Nb/Al-AlOx/Nb Josephsonjunction technology into the nanometer domain and will also be useful for other applications, e.g.,in the quantum domain (higher classical-to-quantum crossover temperature due to higher jc andsmaller junction width).