Negative dynamic conductivity of graphene with optical pumping

Abstract

We study the dynamic ac conductivity of a nonequilibrium two-dimensional electron-hole system in optically pumped graphene. Considering the contribution of both interband and intraband transitions, we demonstrate that at sufficiently strong pumping the population inversion in graphene can lead to the negative net ac conductivity in the terahertz range of frequencies. This effect might be used in graphene-based coherent sources of terahertz radiation.

Broadband graphene terahertz modulators enabled by intraband transitions

“…On the basis of their peculiar band structures, single-layer graphene and Bernal-stacked bilayer graphene have been proposed for novel terahertz [3][4][5][6][7] and optoelectronic devices 8 , with some successful experimental demonstrations [9][10][11][12] . Interband and intraband transitions under optical excitation in graphene have been investigated by various groups [13][14][15][16][17][18][19] .…”

“…The active tuning of terahertz transmission demonstrated in this work suggests that graphene-based structures are attractive for terahertz modulators and electrically reconfigurable filters and attenuators. Free from lattice-matching often required in epitaxial semiconductor heterostructures, these graphene modulators may be easily integrated with existing solid-state continuous wave (CW) terahertz sources such as quantum cascade lasers 31 and resonant tunnelling diode oscillators 32 , and with terahertz detectors such as Schottky diodes 33 and backward diodes 34 , or future graphenebased terahertz emitters and detectors [3][4][5] . The possibilities of facile integration make graphene modulators promising as singlechip solutions for compact and cost-effective transceivers in the terahertz band.…”

Emission of terahertz radiation from two-dimensional electron systems in semiconductor nano-heterostructures

“…Figure 7 presents the carrier relaxation/recombination processes and the non-equilibrium energy distributions of photoelectrons/photoholes at specific times from ~10 fs to few picoseconds after the pumping event [23]. Usually photoexcited carriers are first cooled and thermalized mainly by intraband relaxation processes on femtosecond to subpicosecond time scales, and then by interband recombination processes.…”

“…The gapless and linear energy spectra of electrons and holes lead to nontrivial features such as negative dynamic conductivity. Ryzhii et al analytically revealed that optically pumped graphene can exhibit negative-dynamic conductivity in the THz spectral range [23,24] which may lead to the development of a new type of THz laser [25,26].…”

Optically controlled terahertz filter based on graphene and cross-like metasurface

“…The value of the chemical potential under the influence of optical pumping with the frequency ν pump = Ω/2π and the energy which is more than k B T , is defined as [15]:…”