Research topics

The nanomat group investigates the electronic and vibrational properties of materials, specifically for materials for energy applications and novel generation electronics.

Thermoelectrics are materials which couple differences in temperature and electrical voltage: applying a heat source to one side of a sample will induce a voltage across it, or conversely by applying a voltage the sample can be used to cool one side or heat the other (solid state refrigerators/heaters with no compressors or moving parts). Interest in thermoelectrics has been reignited 15 years ago by demonstrations (first theoretical then experimental) that structuring a material at the nano-scale would enable a dramatic improvement of the thermoelectrical efficiency. The challenge now is to understand the processes, and to find materials which will allow these principles to be scaled up to industrially useful devices.

Phonons and electron-phonon coupling are intimately related to the previous topic: the vibrational properties of molecules and crystals couple to the electronic state. By inducing a deformation of the atomic structure, the electrons respond dynamically – this coupling between electrons and phonons (the particles which correspond to quanta of vibration in a crystal) gives rise to many interesting phenomena such as superconductivity, normal resistivity, thermal resistance, or the Seebeck effect. Using ab initio tools and the ABINIT package one can calculate phonons and electron-phonon coupling to good precision (from less than 10% down to a few % error with respect to experiments).

Attosecond dynamics of electrons and molecules has become a hot topic in the past 5 years: laser technology has gone beyond the femtosecond resolution which was attained in the 1990s, and one can now probe directly the dynamics of electron densities (as opposed to “only” probing the dynamics of the motion of the atoms). Normal motion of atomic nuclei, which includes all traditional chemistry, happens on a picosecond time scale. By going to femtosecond time scales the coupling of different electronic states to the atomic motion can be controlled – one can break chemical bonds or move molecules around. At the attosecond scale, even the electrons can be probed instantaneously, instead of being averaged out over femtoseconds. This regime poses serious challenges both to experiment and theory, where it is very challenging to come up with a unifying picture to understand the multiple configurations and trajectories of the density of electrons, and especially to predict trajectories. Once this becomes possible, one can “program” a chemical reaction or a certain form of catalysis, by sending in an attosecond pulse, and then letting the system evolve. This type of dynamics is necessarily studied with chemists and physicists from many backgrounds, such as materials, condensed matter, atomic and molecular physics, or optics and lasers.

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