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Full-Text Articles in Engineering
Nonlinear Optical Conductivity Of Two-Dimensional Semiconductors With Rashba Spin-Orbit Coupling In Terahertz Regime, Yee Sin Ang, J C. Cao, Chao Zhang
Nonlinear Optical Conductivity Of Two-Dimensional Semiconductors With Rashba Spin-Orbit Coupling In Terahertz Regime, Yee Sin Ang, J C. Cao, Chao Zhang
Yee Sin Ang
We reveal that two-dimensional semiconductors with Rashba spin-orbit interaction (R2DG) exhibit exceptionally strong nonlinear optical response (NOR) in the terahertz frequency regime. The spin-split of the parabolic energy band in R2DG allows strong multiple-photon process to occur via inter-subband mechanism. We show sharp multiple photon edges in the nonlinear conductivity. The edges correspond to the cut-off effect produced by the multiple-photon process. For Rashba coupling parameter of λ R ≈ 10−10 eV m, electric field strength in the order of only 102 V/cm is required for the NOR to dominate over the linear response. Furthermore, the roles of the parabolic …
Klein Tunneling And Cone Transport In Aa-Stacked Bilayer Graphene, Matthew Sanderson, Yee Sin Ang, C Zhang
Klein Tunneling And Cone Transport In Aa-Stacked Bilayer Graphene, Matthew Sanderson, Yee Sin Ang, C Zhang
Yee Sin Ang
We investigate the quantum tunneling of electrons in an AA-stacked bilayer graphene (BLG) n-p junction and n-p-n junction. We show that Klein tunneling of an electron can occur in this system. The quasiparticles are not only chiral but are additionally described by a "cone index." Due to the orthogonality of states with different cone indexes, electron transport across a potential barrier must strictly conserve the cone index, and this leads to the protected cone transport which is unique in AA-stacked BLG. Together with the negative refraction of electrons, electrons residing in different cones can be spatially separated according to their …
Energy Loss Rate Of A Charged Particle In Hgte/(Hgte, Cdte) Quantum Wells, Qinjun Chen, Yee Sin Ang, Xiaolin Wang, R A. Lewis, Chao Zhang
Energy Loss Rate Of A Charged Particle In Hgte/(Hgte, Cdte) Quantum Wells, Qinjun Chen, Yee Sin Ang, Xiaolin Wang, R A. Lewis, Chao Zhang
Yee Sin Ang
The energy loss rate (ELR) of a charged particle in a HgTe/(HgTe, CdTe) quantum well is investigated. We consider scattering of a charged particle by the bulk insulating states in this type of topological insulator. It is found that the ELR characteristics due to the intraband excitation have a linear energy dependence while those due to interband excitation depend on the energy exponentially. An interesting quantitative result is that for a large range of the incident energy, the mean inelastic scattering rate is around a few terahertz.
Chiral-Like Tunneling Of Electrons In Two-Dimensional Semiconductors With Rashba Spin-Orbit Coupling, Yee Sin Ang, Zhongshui Ma, C Zhang
Chiral-Like Tunneling Of Electrons In Two-Dimensional Semiconductors With Rashba Spin-Orbit Coupling, Yee Sin Ang, Zhongshui Ma, C Zhang
Yee Sin Ang
The unusual tunneling effects of massless chiral fermions (mCF) and massive chiral fermions (MCF) in a single layer graphene and bilayer graphene represent some of the most bizarre quantum transport phenomena in condensed matter system. Here we show that in a two-dimensional semiconductor with Rashba spin-orbit coupling (R2DEG), the real-spin chiral-like tunneling of electrons at normal incidence simultaneously exhibits features of mCF and MCF. The parabolic branch of opposite spin in R2DEG crosses at a Dirac-like point and has a band turning point. These features generate transport properties not found in usual two-dimensional electron gas. Albeit its p Berry phase, …
Subgap Optical Conductivity In Semihydrogenated Graphene, Yee Sin Ang, Chao Zhang
Subgap Optical Conductivity In Semihydrogenated Graphene, Yee Sin Ang, Chao Zhang
Yee Sin Ang
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.
Nonlinear Optical Properties Of Bilayer Graphene In Terahertz Regime, Yee Sin Ang, S Sultan, Rodney Vickers, Chao Zhang
Nonlinear Optical Properties Of Bilayer Graphene In Terahertz Regime, Yee Sin Ang, S Sultan, Rodney Vickers, Chao Zhang
Yee Sin Ang
We have carried out a theoretical and computation study of optical response of bilayer graphene in the terahertz regime. It is found that the optical response of bilayer graphene can be significantly enhanced by nonlinear process for fields greater than 1000v/cm. The optical nonlinearity of bilayer graphene persists even in room temperature. This suggests that bilayer graphene can potentially be utilized as a temperature-robust nonlinear material in the terahertz regime.
Intraband Nonlinear Terahertz Waves Absorption Of Gapped Graphene, Asya Tawfiq, Yee Sin Ang, Chao Zhang
Intraband Nonlinear Terahertz Waves Absorption Of Gapped Graphene, Asya Tawfiq, Yee Sin Ang, Chao Zhang
Yee Sin Ang
The effect of bandgap opening on the intraband nonlinear optical response of graphene in terahertz frequency regime is theoretically investigated. The nonlinear optical response of gapped graphene is found to be sensitively influenced by the bandgap level and temperature. © 2012 IEEE.
Strong Nonlinear Optical Response Of Bilayer Graphene In The Terahertz Regime, Yee Sin Ang, Chao Zhang
Strong Nonlinear Optical Response Of Bilayer Graphene In The Terahertz Regime, Yee Sin Ang, Chao Zhang
Yee Sin Ang
We demonstrate that bilayer graphene exhibits strong nonlinear optical response in the terahertz frequency regime.The electric field strength required to generate single-frequency and triple-frequency nonlinear optical responses comparable to the linear optical response is only moderate and can be easily achieved in laboratory.This strong nonlinear optical response persists even in room temperature.This suggests that bilayer graphene can potentially be utilized in nonlinear terahertz photonics
Nonlinear Optical Spectrum Of Bilayer Graphene In The Terahertz Regime, Yee Sin Ang, S. Sultan, Chao Zhang
Nonlinear Optical Spectrum Of Bilayer Graphene In The Terahertz Regime, Yee Sin Ang, S. Sultan, Chao Zhang
Yee Sin Ang
We demonstrate that the nonlinear optical response in bilayer graphene is among the strongest, especially in the important frequency regime of terahertz to far-infrared. Furthermore, we show that both the single frequency and frequency tripled nonlinear response become comparable to the linear response at very moderate electric field. The field strength for the onset of nonlinear effect in bilayer graphene is well within the experimental achievable range in laboratories. Our result suggests that bilayers are preferred structures for developing graphene-based nonlinear photonics and optoelectronics devices.
Nonlinear Optical Spectrum Of Two-Dimensional Electron Gas With Rashba Spin-Orbit Interaction In Thz Frequency Regime, Yee Sin Ang, C Zhang, Qinjun Chen
Nonlinear Optical Spectrum Of Two-Dimensional Electron Gas With Rashba Spin-Orbit Interaction In Thz Frequency Regime, Yee Sin Ang, C Zhang, Qinjun Chen
Yee Sin Ang
We theoretically calculate the nonlinear optical spectrum of two-dimensional electron gas in the presence of Rashba spin-orbit interaction in terahertz frequency regime. For Rashba coupling parameter in the order of 0.4 eVÅ, the nonlinear optical response exceeds the linear response with the application of an external electric field strength in the order of 103 V/cm.
Two-Color Nonlinear Optical Response Of Graphene With Broken Ab-Symmetry, Yee Sin Ang, Chao Zhang
Two-Color Nonlinear Optical Response Of Graphene With Broken Ab-Symmetry, Yee Sin Ang, Chao Zhang
Yee Sin Ang
We demonstrate that the bandgap opening in graphene induced by AB-sublattice symmetry breaking leads to a strong nonlinear optical response for frequencies well below the bandgap where linear response is strictly forbidden. Our result suggests that one type of graphene with such symmetry breaking, semihydrogenated graphene, can have a unique potential as a two-color nonlinear material in the terahertz photonics.
Energy-Loss Rate Of A Fast Particle In Graphene, Yee Sin Ang, Chao Zhang, Chun Kee
Energy-Loss Rate Of A Fast Particle In Graphene, Yee Sin Ang, Chao Zhang, Chun Kee
Yee Sin Ang
The energy-loss rate of a fast particle in graphene is studied. The energy-loss rate always increases with increasing incident particle energy, which is quite unusual when compared to electron gas in normal metal. Graphene exhibits a “discriminating” behavior where there exists a low energy cut-off below which the scattering process is strictly forbidden, leading to lossless traverse of an external particle in graphene. This low energy cutoff is of the order of nearest neighbor hopping bandwidth. Our results suggest that backscattering is also absent in the external particle scattering of graphene.
Nonlinear Optical Response Of Graphene Superlattice In Terahertz Frequency Regime, Yee Sin Ang, Chao Zhang
Nonlinear Optical Response Of Graphene Superlattice In Terahertz Frequency Regime, Yee Sin Ang, Chao Zhang
Yee Sin Ang
We investigate the nonlinear optical response of a Kronig-Penney type graphene superlattice in which the Fermi velocity of the massless Dirac quasiparticle anisotropically depends on the direction of propagation. Such velocity anisotropy results in enhanced nonlinear optical response in terahertz frequency regime.