Session G2: Plenary Session IV

Topological Quantum Numbers and their Importance for Precise Measurements

Various physical quantities can be related to topological invariants. The simplest exampled is the circulation of a superfluid round a circular pipe which is related to the change of the phase of the condensate wave function round the pipe. The Josephson frequency-voltage relation is another example, where the voltage across a weak superconducting link is proportional to the frequency of the alternating current across the link, with very high precision. A more complicated example was provided by the experimental discovery of the quantum Hall effect, where the topological invariant turned out to to a winding over the surface of a torus, rather than around a single loop. Attention in recent years has shifted to topological insulators, but theory and experiment have not yet converged as neatly as they did for the quantum Hall effect.   

New Frontiers in Optical Science: Terahertz Spectroscopy ot Two Dimensional Systems

Terahertz (THz) radiation is electromagnetic radiation whose frequency lies between the microwave and infrared regions of the spectrum. Naturally occurring THz radiation fills up the space of everyday life providing warmth, yet this part of the spectrum remains the least explored region mainly due to the technical difficulties. The technological gap, however, has been rapidly diminishing for the last two decades. The new and exciting frontier of the THz science and technology has encroached on many different disciplines producing a broad range of applications such as medical imaging, sensing of biochemical agents, and ultra-high speed communication. Furthermore, the unique and advanced techniques of the THz spectroscopy have been proved to be a powerful tool to investigate the material properties inaccessible until recently. For example, THz waves strongly interact with electrons and holes in two dimensional systems, in which their dynamics are governed mainly by many-body Coulomb interactions. I will present our experimental studies demonstrating remarkable quantum effects in semiconductor nanostructures and exotic charge carrier dynamics in graphene.