Research expeditions:

• Emission control using valley induced chirality in gapped Dirac systems

In gapped graphene or transition metal dichalcogenides, electrons in the two valleys have opposite Berry curvature, ensured by time-reversal symmetry (TRS) of their chiral Hamiltonians. Hence, far field light scattering coefficients of these system does not differentiate between circularly polarized light, i.e. zero circular dichroism in the classical sense. Optical pumping with circularly polarized light naturally breaks TRS, and a net chirality ensues. However, under typical experimental conditions, the transverse conductivity due to Berry curvature is less than the quantized conductivity minimum  , and the associated optical dichroism effect is not prominent. These effects, however, can be amplified through enhanced light-matter interaction with plasmons. To this end, we have proposed (arXiv:1509.00790, under review) the emergence of new chiral electromagnetic plasmonic modes which can lead to experimentally observable optical dichroism effect. I showed how a generic gapped Dirac system under continuous pumping with positive cicularly polarized light can lead to the appearance of edge chiral plasmons, and how they can allow launching of one-way propagating edge plasmons in a semi-infinite geometry. Through extensive analytical and numerical calculation, the hybridization of these chiral edge modes in a nanoribbons geometry was shown to lead to an all optical valley induced giant Faraday rotation. Since unlike a magnetic field, the field profile of the optical pump can be easily manipulated on the subwavelength scale by the use of nanostructures, our work is expected to pave the way for chip scale nonreciprocal photonics.