Research Topics
 

Condensed matter systems are many-body systems with many phenomena acting and interacting at the same time. In our quest for new quantum limits, we build systems that minimize unwanted interactions and enhance the properties of interest. Oftentimes, this greatly simplifies the underlying theory and facilitates a quantitative understanding from which we can advance to more complex structures.

Spins on surfaces provide a seemingly endless playground for different kinds of phenomena from the challenges of decoupling spins to interacting spins that form the Kondo effect or Yu-Shiba-Rusinov (YSR) states. We aim at manipulating spins on different levels exploiting selection rules in tunneling or in a maximally decoupled environment. We are employing the still new concept of combining electron spin resonance spectroscopy and scanning tunneling microscopy to control single spins and explore their properties.

Feeding microwaves into the tunnel junction provides an additional degree of freedom for manipulating impurity levels, spins or the tunneling process itself. Microwaves facilitate coherent control, which is what we envision in future projects. We have implemented microwave control through an external antenna next to the tunnel junction for frequencies up to 100 GHz. With these new capabilities, we want to not only manipulate spins through electron spin resonance spectroscopy, but also other single level systems to explore coherent control.

At very low temperatures, the tunneling current is no longer a continuous flow of charges, but its granularity has to be taken into account for a quantitative modeling of the experimental data. Charge quantization effects lead to energy exchange with the electromagnetic environment surrounding the tunnel junction, which ultimately limits the energy resolution that can be achieved with a scanning tunneling microscope. Our goal is to find a quantitative understanding of how much of the experiment actually becomes part of the experiment.

In the quest for novel phenomena, designing materials with specific properties plays an important role. As a complement to the real space techniques that we now predominantly use, we also investigate properties of band structures in novel materials using angular resolved photoemission spectroscopy.