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Derivation of Line Shape Function in the Optical Conductivity by a New Diagram Method
摘要： A new diagram method for the line shape function in the optical conductivity formula is introduced and the result obtained applying the method to an electron-phonon system is compared with that derived using the projection-reduction method. The result satisfies the population criterion, which states that the distribution functions for electrons and phonons should be combined in multiplicative forms and gives physical intuition to quantum dynamics of electrons in a solid. This method can be called the "KC diagram" method because it originates from the proper application of the Kang-Choi reduction identity and a state-dependent projection operator.
关键词： line shape function,optical conductivity,diagram method,population criterion,electron-phonon system
更新于2025-09-23 15:22:29
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Profound optical analysis for novel amorphous Cu2FeSnS4 thin films as an absorber layer for thin film solar cells
摘要： In this study, quaternary kesterite Cu2FeSnS4 (CFTS4) has been selected due to its interesting optical and electrical characteristics. The CFTS4 films were prepared by exploiting the chemical bath deposition process at room temperature. The films were prepared at different deposition periods (1, 3, 5 and 7 h). The EDAX technique was helped in evaluating the compositional element ratio which near to 2:1:1:4. The morphology and structure of CFTS4 films have been examined by utilizing X-ray diffraction, and field emission scanning electron microscope techniques. XRD charts revealed the absence of sharp peaks and approved the amorphous nature of films under investigations. The transmittance and reflectance data were employed to compute the linear and nonlinear optical constants of the as-deposited CFTS4 films. The energy gap calculations for the CFTS4 films grown on glass substrate displayed a direct energy gap and by increasing the deposition time, a reduction in energy gap values from 1.41 to 1.19 eV was obtained. The deep analysis of linear/nonlinear optical properties as a function of deposition time has revealed many characteristics of the investigated films. Moreover, the nonlinear parameters (refractive index n2, nonlinear absorption coefficient βc and the third-order nonlinear optical susceptibility χ(3)) of the CFTS4 films were boosted with rising up the film thickness and their high values imply the possibility of utilizing these films in various optoelectronic applications.
关键词： Optical conductivity,Energy gap,Optoelectronic applications,Chemical bath deposition technique,CFTS4 thin films
更新于2025-09-23 15:21:01
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Optical characterization of Peierls instability of zigzag-edge phosphorene nanoribbons
摘要： It has been demonstrated that the bare zigzag-edge phosphorene nanoribbons (zPNRs) were regularly believed as metals. However, some first-principle work [EPL108, 47005 (2014); PRB94, 075422 (2016)] suggested that zPNRs could be Peierls-gapped semiconductor due to the edge-reconstructions. In this work, we study the optical characterization of edge-Peierls-instability (EPI) in zPNRs based on the tight-binding calculations. Responding to EPI, an additional infrared absorption can be observed in the polarized-optical-conductivity-spectrum which is resonant to the Peierls gap. This new peak could be either singlet or doublet, which is determined by the ribbons embracing even- or odd-number zigzag chains. Moreover, it is unraveled that the opening of the Peierls gap is intimately related to the formation of the isolated edge-state subbands near the Fermi level.
关键词： Optical conductivity spectrum,Peierls instability,Tight-binding calculations,Zigzag-edge phosphorene nanoribbons
更新于2025-09-19 17:15:36
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Solvent-free and large-scale preparation of silver@polypyrrole core@shell nanocomposites; structural properties and terahertz spectroscopic studies
摘要： There is a growing interest over the environmental safety and mass-production of polymer nanocomposites. Solvent-free synthetic pathways are considered as promising alternative green techniques because of their high efficiency, simplicity and negligible liberation of hazardous waste. A new synthetic route has been developed to synthesize silver@polypyrrole core@shell nanocomposites at ambient condition. The silver nanoparticles are directly synthesized via solid-state reaction with poly(vinylpyrrolidone) and then pyrrole is polymerized in Ag/PVP powder. The band gap value decreases with the increased addition of pyrrole in the preparation step due to the formation of more silver nanoparticles. Scanning and transmission electron microscope confirm the formation of core@shell structure. The negatively charged carbonyl group of poly(vinylpyrrolidone) can bind to polycationic polypyrrole by an electrostatic effect to form the core@shell structure. The terahertz spectroscopy characterizes the prepared core@shell nanocomposites that are well fit to the Drude-Smith model. The DC optical conductivity in the terahertz range (0.3–2 THz) is increased with increasing Py addition.
关键词： Core@shell,Solvent-free method,Silver,Polypyrrole,Optical conductivity
更新于2025-09-19 17:13:59
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Graphene Photonics || Optoelectronic Properties
摘要： In the preceding chapter, the surface optical conductivity eσeωT of graphene contributed by interband transitions was considered, which characterizes the optical response of graphene in the high-frequency region and has a real part given by (3.106) when the relaxation rate is taken to be zero by ignoring the finite relaxation times of the states involved in the transitions. We find by using this surface optical conductivity that monolayer graphene has an approximately constant absorbance of about 2.3 percent in the optical spectral region. However, in the low-frequency region, the surface optical conductivity eσeωT obtained in the preceding chapter is not valid. For example, if we set ω ? 0 for eσe0T to find the DC surface conductivity, we find that eσe0T is also zero, which is inconsistent with the DC surface conductivity obtained in Chapter 2. The discrepancy comes from the fact that eσeωT given in the preceding chapter only accounts for interband absorption of photons with electrons making transitions from a valence band to a conduction band, whereas the DC surface conductivity given in Chapter 2 is solely contributed by the intraband transitions of charge carriers within a valence band or within a conduction band.
关键词： Optoelectronic Properties,Surface Optical Conductivity,Intraband Transitions,Graphene,Interband Transitions
更新于2025-09-16 10:30:52
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Optical properties of fluidic defect states in one-dimensional graphene-based photonic crystal biosensors: visible and infrared Hall regime sensing
摘要： Advances in biotechnology are outpacing studies into the use of graphene in photonic biosensors due to its peculiar optical properties and the successful progress in the nanoscale integration of photonic crystals. Moreover, going beyond the usual Dirac cone approximation for graphene introduces nonlinear effects in graphene’s optics. In this work, by the use of the transfer matrix method, we investigate the effect of hopping parameter on the chemical and biosensing performance of a 1D defective photonic biosensor with a micro/nano?uidic channel as a central defect cavity for biological ?uids and gas molecules to ?ow while interacting with two graphene sheet deposited on silicon dioxide layers of the device. As low-weight molecules absorption on graphene’s surface could affect hopping energy of graphene which plays a signi?cant role in its optical conductivity obtained from the tight-binding model for the visible range, it will serve as a promising tool for the detection of gas and other analytes. We also examine the sensitivity of the defect modes to the changes of the refractive index of the biological ?uids under the in?uence of quantum Hall situation for graphene in terahertz (THz) regime. It is revealed that two defective modes with relatively different sensing properties are emerged within the band stop of the device. The results of this study are not reported elsewhere to the best of our knowledge.
关键词： photonic crystal,hopping parameter,terahertz,biosensor,optical conductivity,visible light,graphene,quantum Hall effect
更新于2025-09-16 10:30:52
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Light-Induced Current Oscillations in the Charge-Ordered State of (TMTTF)2SbF6
摘要： Below TCO = 157 K the quasi-one-dimensional charge-transfer salt (TMTTF)2SbF6 undergoes a pronounced phase transition to a charge-ordered ground state. We have explored the non-linear and photoconductive behavior as a function of applied voltage, laser pulse energy and temperature. Besides a decay of the photoconductive signal in a double exponential fashion in the millisecond range, we discover current oscillations in the kHz range induced by the application of short laser pulses. While the resonance frequencies do not depend on voltage or laser intensity and vary only slightly with temperature, the amplitude changes linearly with the laser intensity and voltage. We suggest that photo-induced fluctuations of the charge-ordered state alter the current flow of the single particles and hence, the photocurrent. The findings are discussed and compared to comparable phenomena in other low-dimensional electron systems.
关键词： TMTTF,non-linear transport,calculations of band structure and optical conductivity,charge-transfer salts,photoconductivity,current oscillations,charge-order phase transition
更新于2025-09-11 14:12:44
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Optical conductivity and transparency in an effective model for graphene
摘要： Motivated by experiments confirming that the optical transparency of graphene is defined through the fine structure constant and that it could be fully explained within the relativistic Dirac fermions in a two-dimensional picture, we investigate in this article how this property is affected by next-to-nearest-neighbor coupling in the low-energy continuum description of graphene. A detailed calculation within the linear response regime allows us to conclude that, somewhat surprisingly, the optical conductivity at zero temperature that determines the transparency remains robust up to this correction.
关键词： graphene,optical conductivity,linear response,transparency,Dirac fermions
更新于2025-09-10 09:29:36
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Free-carrier dynamics in Au <sub/>2</sub> Pb probed by optical conductivity measurements
摘要： We measured the optical reflectivity of the Dirac material Au2Pb in a broad frequency range (30–48 000 cm?1) for temperatures between 9 and 300 K. The optical conductivity, computed from the reflectivity, is dominated by free-carrier contributions from topologically trivial bulk bands at all temperatures. The temperature-independent total plasma frequency of these carriers is 3.9 ± 0.2 eV. Overall, optical response of Au2Pb is typically metallic with no signs of localization and bad-metal behavior.
关键词： topological semimetals,optical conductivity,Dirac materials
更新于2025-09-10 09:29:36
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Spectroscopic signature of trimer Mott insulator and charge disproportionation in
摘要： We have measured the re?ectivity spectra of the barium iridate 9R BaIrO3, the crystal structure of which consists of characteristic Ir3O12 trimers. In the high-temperature phase above the transition temperature Tc (cid:2) 180 K, we ?nd that the optical conductivity involves two temperature-dependent optical transitions with an ill-de?ned Drude response. These features are reminiscent of the optical spectra in the organic dimer Mott insulators, implying a possible emergence of an unusual electronic state named trimer Mott insulator in BaIrO3, where the carrier is localized on the trimer owing to the strong Coulomb repulsion. Along with a pronounced splitting of the phonon peak observed below Tc, which is a hallmark of charge disproportionation, we discuss a possible phase transition from the trimer Mott insulator to a charge-ordered insulating phase in BaIrO3.
关键词： phase transition,charge disproportionation,BaIrO3,optical conductivity,trimer Mott insulator
更新于2025-09-10 09:29:36