Quantum Theory of the Solid State
Solids are, per definition, many-particle systems, and most techniques we use were originally developed to study the properties of solids such as optical response, magnetism and superconductivity. The models from solid state physics are being tested more and more often using ultracold atomic gases which makes a link with the other research direction in the group. But we definitely remain very active in traditional solid state physics as well – a selection of the subjects we study can be found below:
- Nanoscopic superconductivity: When superconductors are constructed on the nanometer scale, or when nanoscopic patterns are created, their properties will change from those of bulk superconductors. In particular the critical fields become higher and there is more control over the movement of vortices. On this subject we closely collaborate with the experimental group of prof. V. Moshchalkov at the KULeuven. Their expertise in producing nanoscopic and mesoscopic superconducting parts nicely complements our theoretical techniques – especially in the time-dependent Ginzburg-Landau formalism – very well.
- Modeling of unconventional superconductors: Not all superconductors can be understood using the microscopic theory of Bardeen, Cooper and Schrieffer. For some materials, a more detailed descriptions is necessary, one that, for example, includes the inter-plane phonons explicitly. For instance, this is important in the recently discovered effect that (insulating) LaAlO placed on (insulating) SrTiO gives rise to a superconducting inter-plane. We are developing the theory for this system in collaboration with several experimental groups (among others with the group of prof. Van der Marel at the university of Genève).
- Optic response of metallic nanoparticles: That small metallic spheres scatter light in specific colours was already known by the ancient Romans using metallic spheres to create coloured glass. The traditional description of the optical response of nanoparticles is very ‘classical’ in the sense that it does not include quantum effects for the electric charges in the metal. This is what we do try to do, and at the same time look for nanoparticles where the quantum effects are important.