Subgap optical conductivity in semihydrogenated graphene

Abstract

We report that for graphene with a finite band gap (such as semihydrogenated graphene or graphene with spin-orbit coupling), there exists a strong nonlinear optical response for energies lower than the band gap where the linear response is forbidden. At low temperatures, the nonlinear current in graphene with a gap is much stronger than that in gapless graphene. Our result suggests that semihydrogenated graphene can have a unique potential as a two-color nonlinear material in the terahertz frequency region. The relative intensity of the two colors can be tuned with the electric field.

Room-temperature strong terahertz photon mixing in graphene

“…Unfortunately, nonlinear optical effects in conventional semiconductors are usually minimal unless an extremely intense laser pulse is applied, and this greatly reduces the practicality of semiconductor-based devices. Recently, it has been demonstrated that the nonlinear optical response in graphene and several sister structures can be rather strong, especially in the important terahertz frequency regime [15][16][17][18][19][20][21][22][23]. For single layer graphene, strong terahertz interband [15] and intraband [16,17] nonlinear optical responses were theoretically predicted.…”

Nonlinear graphene plasmonics

“…Perturbative models are developed to supplement the interband physics, for example the quantum mechanical (QM) Dirac equation model [61,62,64,66,67,89], and also the semiconductor Bloch equations [73,75,76,85]. The QM model replaces v g in equation (3.1) with v g = ψ|∂ H/∂k|ψ , where ψ is the wave function of graphene and H is the Dirac Hamiltonian, which replaces N(p) with N(p) = f (−ε k ) − f (ε k ), the Fermi distribution difference between the conduction and valence bands.…”

Temperature-dependent of Nonlinear Optical Conductance of Graphene-based Systems in High-intensity Terahertz Field

“…The optical properties of graphene have been studied both experimentally [9][10][11][12][13][14][15][16][17] and theoretically [18][19][20][21][22][23][24][25][26][27][28][29][30]. In the terahertz to the far-infrared (FIR) spectral regime, optical conductance of graphene-based systems attracts many researchers' interests due to the ongoing search on viable terahertz detectors and emitters.…”

“…Zhou et al [25] also treated the same topic with more rigorous perturbation theory. Yee Sin Ang et al [28,29] investigated the optical conductivity of SHG and KP graphene superlattic. It has been shown that SHG possesses a unique potential as a two-color nonlinear material and the total optical response of the graphene superlattice was enhanced due to the formation of anisotropic Dirac fermions in the terahertz frequency region.…”

“…This may make graphene as a simple and natural frequency multiplier and open up exciting opportunities for using graphene in terahertz electronics. Subsequently, a series of theoretical works were carried out to seek for the strong nonlinear terahertz responses of graphene-based systems, such as single layer graphene (SLG) [23][24][25], bilayer graphene (BLG) [26], graphene p-n junction [27], graphene nanoribbons (GNRs) [28], semihydrogenated graphene (SHG) [29] and Kronig-Penney type (KP) graphene superlattice [30]. As studied by Hendry et al in 2010 [15], they first measured the coherent nonlinear optical response of single-and few-layer graphene using four-wave mixing.…”