Negative differential transmission in graphene

TL;DR

This paper investigates the mechanisms behind negative differential transmission in graphene using Kubo linear response theory, revealing conditions related to electron distribution, temperature, and conductivity components that lead to this phenomenon.

Contribution

It provides a detailed theoretical analysis of negative differential transmission in graphene, highlighting the roles of intra- and inter-band conductivity, electron distribution, and many-body effects.

Findings

Negative differential transmission occurs at low and high probe-photon energies.

Intra-band conductivity increase causes negative transmission at low energies.

Inter-band contributions involve Hartree-Fock self-energy and scattering effects.

Abstract

By using the Kubo linear response theory with the Keldysh Green function approach, we investigate the mechanism leading to the negative differential transmission in system with the equilibrium electron density much smaller than the photon-excited one. It is shown that the negative differential transmission can appear at low probe-photon energy (in the order of the scattering rate) or at high energy (much larger than the scattering rate). For the low probe-photon energy case, the negative differential transmission is found to come from the increase of the intra-band conductivity due to the large variation of electron distribution after the pumping. As for the high probe-photon energy case, the negative differential transmission is shown to tend to appear with the hot-electron temperature being closer to the equilibrium one and the chemical potential higher than the equilibrium one but considerably smaller than half of the probe-photon energy. We also show that this negative differential transmission can come from both the inter- and the intra-band components of the conductivity. Especially, for the inter-band component, its contribution to the negative differential transmission is shown to come from both the Hartree-Fock self-energy and the scattering. Furthermore, the influence of the Coulomb-hole self-energy is also addressed.