Light-matter interaction in two dimensional systems

Graphene-like two dimensional semiconductors are promising materials for their intriguing electronic as well as optical properties. In this talk I will give an overview of some of the recent development in this field. I will consider atomically thick layers of transition metal dichalcogenides, which are direct bandgap semiconductors with large binding energy oflonglived excitons. Strong light-matter interaction can be achieved using an optical microcavity to realize exciton-polaritons in this system. The ultralow mass of polaritons makes it a promising candidate to realize the polariton condensation and superfluidity at temperatures close to room temperature. I will present some of our experimental results where we directly probe the polariton energy band dispersion by angle resolved spectroscopy. A finite electron density in the system give rise to charged-excitons or trions which are like stable hydrogen ions. We observed that the dispersion of trion-polariton branch deviates from its expected characteristics as understood from a coupled harmonic oscillator model. The anomalous dispersion that we observed can be understood by considering interaction between the polariton branches mediated by free electrons in the system. The exciton-polaritons in this new material system can provide a playground to study non-equilibrium manybody physics.