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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Excitonic Effects in Single Layer MoS <sub/>2</sub> Probed by Broadband Two-Dimensional Electronic Spectroscopy
摘要： Atomically thin Transition-metal dichalcogenides (TMDs) have come into the spotlight in optoelectronics thanks to their outstanding physical properties. In single-layer (1L) TMDs strong quantum confinement effects cause a weak screening of Coulomb, so that the excitons created by photo-excitation have large binding energy, up to several hundred meVs. While the steady-state properties of TMDCs have been studied in detail by linear optical techniques, the recent application of time-resolved nonlinear spectroscopy (mainly ultrafast pump-probe) has enabled the study of excited-state dynamics on femtosecond timescales opening up questions about the mechanisms of exciton relaxations and exciton-exciton interactions. Among TMDs, the spectrum of 1L MoS2 is characterized by two peaks of excitonic nature in the visible spectral region (1.9 eV and 2.05 eV), the so-called A and B excitons. They arise from optical transitions between the spin?orbit split top valence band and the bottom conduction band, around K and K’. Here we use two-dimensional electronic spectroscopy (2DES) to track the sub-ps excitonic interactions within 1L MoS2. We report 2DES measurements obtained on a chemical vapor deposition grown 1L MoS2 sample, at 77K, using sub 20-fs broadband pulses. Thanks to its unique combination of high temporal and spectral resolution, 2DES provides a series of excitation/detection correlation energy maps at different delays T, simultaneously covering the A and B excitons.
关键词： excitonic effects,MoS2,Transition-metal dichalcogenides,two-dimensional electronic spectroscopy
更新于2025-09-12 10:27:22
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Excitonic effects on layer- and strain-dependent optoelectronic properties of PbI2
摘要： Exciton states have obvious effects on optical properties of two-dimensional (2D) materials. Here, we investigate excitonic effects on electronic and optical properties of PbI2 by using GW + Bethe-Salpeter equation method, considering the layer number and strain effect. These studies show that exciton states obviously modify and dominate the optical absorption of 2D PbI2 nanosheets. Also, with the increasing number of layers, the intensity of main absorption peak increases and the exciton binding energy decreases. Meanwhile, the tensile strain can induce the threshold energy of optical spectra shift down the low energy, and exciton binding energy has a maximum at the strain of 3%. Therefore, our results indicate that the 2D PbI2 nanomaterials have excellent ultraviolet absorption and corresponding potential for the application of optoelectronic devices.
关键词： Optical property,Electronic structure,Lead iodide,Excitonic effects,Two-dimensional semiconductor
更新于2025-09-09 09:28:46
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High energy shift in the optical conductivity spectrum of the bilayer graphene
摘要： We calculate theoretically the optical conductivity in the bilayer graphene by considering Kubo-Green-Matsubara formalism. Different regimes of the interlayer coupling parameter have been considered in the paper. We show that the excitonic effects substantially affect the optical conductivity spectrum at the high-frequency regime when considering the full interaction bandwidth, leading to a total suppression of the usual Drude intraband optical transition channels and by creating a new type of optical gap. We discuss the role of the interlayer coupling parameter and the Fermi level on the conductivity spectrum, going far beyond the usual tight-binding approximation scheme for the extrinsic bilayer graphene.
关键词： interlayer coupling,excitonic effects,Kubo-Green-Matsubara formalism,bilayer graphene,optical conductivity
更新于2025-09-04 15:30:14