In recent years a new class of layered solids known as “transition metal dichalcogenides” have been uncovered, which exhibit novel physical properties attractive for electronic and photonic applications. These include ultra-efficient field effect transistors, super sensitive photo-detectors, and extreme optical nonlinearities, enabling the easy generation of high harmonic frequencies.
Typical transition metals of interest are single atomic layers of molybdenum disulfide (MoS2) and tungsten diselenide (WSe2), which have direct band gaps, and an electronic dispersion which can be described using variants of the relativistic Dirac equation. Such a single layer can absorb between 5% and 10% of any incident light - an enormous amount considering its thinness.
The first aim of this project is to gain a theoretical understanding of the excitonic states in Dirac-like transition metals. These have been shown to possess very large electron-hole binding energies which could therefore be observed and exploited at room temperature. Excitons in these materials will likely behave differently from traditional semiconductor excitons, as their wavefunction is governed by the Dirac equation, rather than the Schroedinger equation, and new physics is expected to emerge.
The further aim of the project is to study the enormous optical nonlinearities in transition metals. The generation of electrically controlled second harmonics has been recently reported, but a full theoretical understanding of the nonlinear optical effects in 2D Dirac-like materials is still lacking, and these materials offer great opportunities for new discoveries.