Current Research / Recherche actuelle :
In the framework of the QuEST activity, our research covers the topics: Superconductivity at Nanoscale, and Novel Quantum Materials and Phenomena. In our experimental studies at low temperatures and in ultrahigh vacuum we use two complementary surface-sensitive approaches: High-resolution Scanning Microscopy and Spectroscopy (Tunneling, Kelvin Probe, Josephson etc.) and Angle-Resolved Photo-Emission Spectroscopy (ARPES).
Superconductivity at Nanoscale
Novel phenomena emerge when dimensions of a superconducting material are reduced down to the coherence length of Cooper pairs. At yet lower size, reaching the atomic limit, some materials lose their superconducting properties and becomes metals or insulators, whereas others, non-superconducting in the bulk, become superconducting and acquire unexpected properties.
|Proximity phenomena in hybrid superconducting systems.|
When a Cooper pair penetrates from a superconductor into a normal metal N, it becomes a pair of time-reversed electron states that propagate coherently in N. The propagation of superconducting correlations inside novel materials such as grapheme, topological insulators, semi-metals, Mott insulators etc. is strongly affected by remarkable quantum properties of these materials.
|Near-critical superconducting states.|
Increasing the intensity of dissipation-less electric current in a superconductor weakens the superconductivity; at a critical current value the superconductivity is destroyed. Owing a combination of local scanning tunneling microscopy/spectroscopy and global transport measurements of a current-carrying superconducting nanowire, we dress the microscopic picture of the critical superconducting state close to the phase transition.
Novel Quantum Materials and Phenomena
|Spin-orbit interactions at surfaces.|
Electron-electron correlations, electron-phonon interactions, Rashba spin-orbit coupling and band bending effects in Mott, charge density waves and superconducting phases produce electron energy gaps, distortions and periodic electronic features in the real and reciprocal spaces. These phenomena are revealed in single atomic metallic layers on semiconductors by means of scanning tunneling microscopy and spectroscopy, angle resolved photoelectron spectroscopy, atomic force microscopy and state-of-the-art density functional and dynamical mean field theory calculations.
|Insulator-metal phase transitions: bulk, surfaces and interfaces.|
Microscopic description of the Mott Metal-to-Insulator transition is one of major challenges of modern Condensed Matter physics. Usually, the transition is obtained by changing temperature or pressure. Some transition metal chalcogenures are fragile Mott insulators: A remnant transition into a metallic state may be induced there by applying electric field, resulting in a dramatic change in the resistivity of the material. This remarkable macroscopic phenomenon still lacks a microscopic understanding.