STS-CS experimentally investigates model 2D systems with strong electron correlation effects simple enough to be addressed by "first principle" state-of-the-art calculations.
The lab has a system for scanning tunneling spectroscopy and microscopy (STM-STS) in ultra-high vacuum at low temperature (minimum sample temperature 7 K) with a liquid He cryostat. The system has a sample preparation chamber with facilities for ion bombardment, LEED, evaporation, annealing, and a manipulator that can be cooled at 25 K. The STM and several parts of the system are home-made.
The research activity is focused on the experimental study of model systems on surfaces in which electron correlation effects are important. The systems are simple enough to allow to test if state-of-the-art ab-initio-based theories are able to make accurate quantitative predictions of their properties.
We studied by STS and other techniques some surfaces with an odd number of electrons per unit cell demonstrating that, is some cases, they undergo metal-insulator Mott-Hubbard transitions predicted by LDA+U calculations by other theoretical groups (SISSA), and in a temperature range estimated by the simulations. In other cases there are discrepancies between experimental and theoretical results.
Choosing a simple and exemplary spin 1/2 molecular radical physisorbed on a suitable metal, we have shown that it presents a zero bias Kondo anomaly in low-temperature STS, in agreement with calculations based on a combination of density functional theory and numerical renormalization group (DFT+NRG) . The comparison of the experimental and computational results provides a measure of the approximations used in the modeling of the Kondo state.
