Exciton oscillator strength in two-dimensional Dirac materials

Sommerfeld enhancement factor in two-dimensional Dirac materials

“…As well as in Ref. [19] we consider a two-valley 2D Dirac semiconductor with the valleys K and K which are time-reversal of each other. The components ψ ++ , ψ +− , ψ −+ , ψ −− of the electron-hole-pair wave functions are conveniently presented as a four-component vector Ψ exc .…”

“…The components ψ ++ , ψ +− , ψ −+ , ψ −− of the electron-hole-pair wave functions are conveniently presented as a four-component vector Ψ exc . For the direct-gap excitations with the electron lying in the K valley and the hole lying in the K valley, the vector Ψ exc satisfies the two-particle Schrödinger equation [19]…”

“…Note that we assume the normal incidence of the exciting light in which case k h = −k e and the pair momentum (k e + k h ) is zero. In the representation (6) the optical absorption matrix element is given by [19] M…”

“…Nowadays, the research interest is focused on excitons in the 2D Dirac materials, with the charge carriers being well described by the 2D Dirac equation and the electron-hole interaction energy being less but comparable to the energy gap E g [12,13]. In this case, the exciton wave function is described by four components ψ λe,λ h (λ e = ±, λ h = ±) with the electron and the hole having both signs of energy, including the case when they both are in the conduc-tion band (λ e = +, λ h = −) or in the valence band (λ e = −, λ h = +) [14][15][16][17][18][19].…”

“…[19], a theory of the bound-exciton oscillator strength has been developed accounting for the conduction-valence band coupling in the 2D Dirac model and the four-component structure of the exciton wave function. In the present work, we extend the theory [19] and study how the interaction affects the optical matrix elements and absorption above the band edge of the 2D Dirac materials. Earlier, the study of the effect of nonparabolicity on absorption spectra was carried out in Refs.…”