We recently extended our STM studies to the sub-K temperature range in magnetic fields of arbitrary orientation. To this end we set up a new ³He-cooled scanning tunneling microscope with a vector magnetic field to study field-dependent spectroscopic properties of individual nanostructures at temperatures as low as 0.3 K. We envision investigations of the interplay between superconductivity and ferromagnetism at the nanoscale. In connection with theory we aim for a deeper understanding on the electronic level of electron correlation effects in the presence of competing electronic interactions.

Spectra of the differential conductance of 80 ML Pb on Cu(111) measured with a Nb tip at 0.35 K. The red data points reveal a drop of the differential conductance around a gap voltage between tip and sample of 0 mV, and sharp increase at +/- 1 mV. This spectroscopic feature is the hallmark of superconductivity of this system. The application of a magnetic field of 3.5 T along the tip axis, perpendicular to the sample surface, removes this so-called superconducting gap. In contrast to the measurements in zero field (red curve), now an almost constant differential conductance is observed (blue curve), indicative of a state of normal conductivity of the system.