Abstract
The existence of moving indirect excitons in monolayer graphene is theoretically evidenced in the envelope-function approximation. The excitons are formed from electrons and holes near the opposite conic points. The electron-hole binding is conditioned by the trigonal warping of the electron spectrum. It is stated that the exciton exists in some sectors of the exciton momentum space and has the strong trigonal warping of the spectrum.
Highlights
An exciton is a usual two-particle state of semiconductors
The absence of the gap makes this picture inapplicable to graphene, and the immobile exciton becomes impossible in a material with zero gap
We use the term ‘exciton’ in its direct meaning, unlike other papers where this term is referred to as many-body (‘excitonic’) effects [1,2], exciton insulator with full spectrum reconstruction, or exciton-like singularities originating from saddle points of the single-particle spectrum [3]
Summary
An exciton is a usual two-particle state of semiconductors. The electron-hole attraction decreases the excitation energy compared to independent particles producing the bound states in the bandgap of a semiconductor. The absence of the gap makes this picture inapplicable to graphene, and the immobile exciton becomes impossible in a material with zero gap. The purpose of the present paper is an envelopeapproximation study of the possibility of the WannierMott exciton formation near the conic point in a neutral graphene. There is a widely accepted opinion that zero gap in graphene forbids the Mott exciton states (see, e.g., [4]). This statement which is valid in the conic approximation proves to be incorrect beyond this approximation.
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