STM / STS on strongly correlated electron systems
Strongly correlated electron systems, i.e. materials in which the electrons strongly interact with each other, exhibit a plethora of fascinating phenomena including unconventional superconductivity and quantum criticality, many of which are not yet fully understood. However, to gain further insight, comprehensive investigations of thermodynamic and transport properties of these materials at low temperature are called for.
We have set up Scanning Tunneling Microscopy (STM) which is an established powerful tool to investigate the electronic structure of materials. In an effort to optimize sensitivity for the materials and phenomena in quest we can conduct STM in UHV, down to 310 mK and in applied magnetic fields of up to 12 T. These investigations are complemented by magnetotransport measurements down to 40 mK. With these tools, we observed phenomena ranging from electronic phase separation at the metal-to-insulator transition in manganites to the coexistence of superconductivity and antiferromagnetic order in Ce-based heavy fermion metals. Recently, we focus our research on the investigation of the hybridization of conduction and 4f electrons as well as the formation of Kondo coherence in Kondo metals and insulators.
At present we are extending these measurements to investigate the fade of the Kondo quasiparticles upon approaching a quantum critical point and the nature of the surface states in certain hexaborid Kondo insulators. Specifically for our STM project, we invite students to actively participate in our ongoing research. We have established collaboration with the STM group of Dr. P. Wahl at the University of St. Andrews and consequently, and hence, joint projects could be envisioned.