Many body exciton due to Fano resonance in graphene

Abstract

The excitonic effect is thought to be generally unimportant in zero gap systems (at K point of the Brillouin zone) like monolayer graphene, but excitonic transition in graphene at the saddle point (M) of Brillouin zone has received increasing attentions. There are two important issues with excitons in graphene. Firstly: in contrast to excitonic transitions in semiconductors the line shape of excitonic peaks in graphene is asymmetric which is due to Fano resonance, a many body coupling between discrete excitonic state and continuous band states, Secondly due to many body effects the excitonic peak is sensitive to dielectric environment. Hence it is desirable to vary the dielectric environment of graphene without varying carrier concentration. To investigate this completely new method for obtaining graphene monolayer has been developed using chemical exfoliation technique. We show that there is shift in excitonic peak position with change in the dielectric environment of graphene and this has been achieved by varying Fermi velocity without varying the carrier concentration. The observed distinctive effect is decrease in exciton binding energy with increase in dielectric value of exfoliating solvents, resulting into a scaling relation between the dielectric environment and the exciton binding energy of graphene.