In this joint research effort, the aim is to explore supported model systems at the atomic scale to study electronic correlation, coherence and entanglement effects as a function of a continuously tunable interaction. These model systems have the benefit of usually being sufficiently simple to still describe them theoretically and test the relevant theoretical predictions on them.

On the other hand, the basic physics of many bulk correlated electron systems can be mapped onto models consisting only of a few interacting spin centres. Thus the ability to prepare such model systems also provides a direct connection to studies of coherence and entanglement in the quantum criticality in bulk materials. Some of the model systems also share physics with that of cold atoms in lattices, so this project can provide intellectual linkage between several of the projects of the IMPP.

It is envisioned that to this end, UHV (ultra high vacuum) prepared surface supported model systems will be studied at Max Planck Institute for Solid State Research in Stuttgart at low temperature by scanning tunneling microscopy and spectroscopy. These studies will be complemented at the University of St. Andrews by investigations by spectroscopic imaging STM (Scanning tunnel microscope) of cleaved bulk samples of correlated electron materials, which cannot be prepared by standard UHV techniques. The joint expertise of both activities has in the past been very successful.

The Max Planck Institute for Solid State Research has outstanding expertise in surface prepared nanostructures, which will allow to construct either nanostructures at the surface with tunable interactions, e.g. by growing metal-organic coordination networks with embedded metal atoms, or by using just single atoms or molecules as magnetic impurities, reducing the problem from a periodic one to a few body problem.

The expertise at University of St. Andrews is in tunneling spectroscopy of correlated electron systems, predominantly prepared in cryogenic vacuum. In these systems, typically bulk properties can be tuned by some external parameter. Thus the facilities in Stuttgart and St. Andrews complement each other. The project would benefit further from linkages between University of St. Andrews and Max Planck Institute for Chemical Physics of Solids in Dresden, and from exchange of ideas with the quantum optics groups in the collaboration.

Both sites have (will have) state of the art low vibration facilities, a prerequisite to perform cutting edge research in the field of tunable model systems for correlated electrons by scanning probe techniques. The mechanical stability required for these measurements demands that the tip-surface distance is kept stable within less than 200fm over extended periods of time, which comes close to dimensions where quantum effects predicted in some of the cosmological theories play a role.

As part of the proposed Partnership, the potential of using this ultra-high stability to test predictions of cosmological theories can be further addressed.