Investigation of nanoscale superconductor-ferromagnet hybrids using very low temperature STS

We investigate laterally structured superconductor-ferromagnet hybrids using a very low temperature STM. A STM is the ideal instrument to investigate the quasiparticle density of states (DOS) with high lateral resolution.The DOS in the superconductor is influenced by proximity effect as well as by the electromagnetic interaction with the ferromagnet. In an external magnetic field B, this can lead to interesting effects such as the oscillatory dependence of the critical temperature on B or the nonuniform nucleation of superconductivity. The proximity effect can be suppressed by spatial separation of the superconductor from the ferromagnet using an insulating layer. We present first results obtained on arrays of ferromagnetic Co dots covered by Al as a superconductor.