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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Optical Properties of Silicene and Related Materials from First Principles
摘要： Slightly buckled, graphene-like honeycomb crystals made by silicon, silicene, or by other group-IV elements such as germanene and stanene represent atomically thin films, i.e., two-dimensional (2D) systems. The theoretical description of their optical properties suffers from three difficulties, (i) a thickness much smaller than the wavelength of light, (ii) their common modeling by superlattice arrangements with sufficiently large layer distances, and (iii) the inclusion of many-body effects. Here, the solutions of all problems are discussed. (i) The optical response of an individual honeycomb crystal is described by a tensor of 2D optical conductivities or dielectric functions, which are related to the optical response of the corresponding superlattice. (ii) The influence of such a sheet crystal on the transmittance, reflectance and absorbance of a layer system is described. (iii) Excitonic and quasiparticle effects are demonstrated to widely cancel each other. Silicene sheets are investigated in detail. As a consequence of the linear bands and Dirac cones the low-frequency absorbance is defined by the Sommerfeld finestructure constant. Van Hove singularities represented by critical points in the interband structure are identified at higher photon energies. Clear chemical trends along the row C → Si → Ge → Sn are derived. The influence of multiple layers is studied for the cases of bilayer silicene and graphene.
关键词： silicene,optical properties,many-body effects,two-dimensional materials,first principles,Van Hove singularities,stanene,Dirac cones,germanene
更新于2025-09-23 15:21:21
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Monte Carlo model incorporating many-body effects for determining the gain spectra of quantum dot lasers
摘要： We present a Monte Carlo model that simulates the gain spectra of a QD laser material that empirically includes free-carrier effects. We compare simulation results of both Fermi–Dirac and random carrier populations, and compare them with experimental data. The free-carrier effects are highlighted as being more important than the choice of carrier statistics, and routes to improve this simple model are discussed.
关键词： many-body effects,free-carrier effects,Monte Carlo model,gain spectra,quantum dot lasers
更新于2025-09-11 14:15:04
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Plasmon-pole approximation for many-body effects in extrinsic graphene
摘要： We develop the plasmon-pole approximation (PPA) theory for calculating the carrier self-energy of extrinsic graphene as a function of doping density within analytical approximations to the GW random phase approximation (GW -RPA). Our calculated self-energy shows excellent quantitative agreement with the corresponding full GW -RPA calculation results in spite of the simplicity of the PPA, establishing the general validity of the plasmon-pole approximation scheme. We also provide a comparison between the PPA and the hydrodynamic approximation in graphene, and comment on the experimental implications of our ?ndings.
关键词： plasmon-pole approximation,self-energy,graphene,GW-RPA,many-body effects
更新于2025-09-11 14:15:04
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Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides
摘要： Monolayer transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) semiconductors for application in optoelectronics. Their optical properties are dominated by two series of photo-excited exciton states—A (XA) and B (XB)1,2—that are derived from direct interband transitions near the band extrema. These exciton states have large binding energies and strong optical absorption3–6, and form an ideal system to investigate many-body effects in low dimensions. Because spin–orbit coupling causes a large splitting between bands of opposite spins, XA and XB are usually treated as spin-polarized Ising excitons, each arising from interactions within a specific set of states induced by interband transitions between pairs of either spin-up or spin-down bands (TA or TB). Here, by using monolayer MoS2 as a prototypical system and solving the first-principles Bethe–Salpeter equations, we demonstrate a strong intravalley exchange interaction between TA and TB, indicating that XA and XB are mixed states instead of pure Ising excitons. Using 2D electronic spectroscopy, we observe that an optical excitation of the lower-energy TA induces a population of the higher-energy TB, manifesting the intravalley exchange interaction. This work elucidates the dynamics of exciton formation in monolayer TMDCs, and sheds light on many-body effects in 2D materials.
关键词： intravalley exchange interaction,2D electronic spectroscopy,exciton states,many-body effects,monolayer transition metal dichalcogenides
更新于2025-09-04 15:30:14