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Optical spectrum of ferrovalley materials:A case study of Janus H-VSSe

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Chinese Physics B 2024年第1期33卷 54-59页

作者：罗朝波刘文超彭向阳 Hunan Key Laboratory for Micro-Nano Energy Materials and Devices School of Physics and OptoelectronicsXiangtan UniversityXiangtan 411105China

As opposed to the prototypical MoS2 with centroasymmetry,Janus ferrovalley materials such as H-VSSe are less symmetric with the mirror symmetry and time reversal symmetry broken,and hence possess spontaneous valley polarization and strong ferroelasticity.The optical transition is an important means to excite the valley carriers.We investigate the optical spectrum of H-VSSe by using the many-body perturbation-based GW approach and solving the Bethe–Salpeter equation(BSE)to include the electron–hole interactions.It is found that after the GW correction,the band gaps of the quasiparticle bands are much larger than those obtained by the normal density functional theory.The system is ferromagnetic and the valley gaps become non-degenerate due to spin–orbit coupling(SOC).The position of the lowest BSE peak is much lower than the quasiparticle band gap,indicating that the excitonic effect is large.The peak is split into two peaks by the SOC.The binding energy difference between these two BSE peaks is about the same as the difference between the inequivalent valley gaps.Our results show that in Janus H-VSSe the two lowest exciton peaks are from the two inequivalent valleys with different gaps,in contrast to the A and B exciton peaks of MoS2 which are from the same valley.

关键词： infrared spectroscopy magnetic topological insulator drude model band reconstruction

Ultraslow electron-phonon scattering and polaron formation in magnetite

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Journal of Materiomics 2022年第1期8卷 150-155页

作者： Adrian Radoń DariuszŁukowiec Patryk Włodarczyk Łukasiewicz Research Network-Institute of Non-Ferrous Metals Sowinskiego 5 St.44-100GliwicePoland Faculty of Mechanical Engineering Silesian University of TechnologyKonarskiego 18 a St.44-100GliwicePoland

The comprehensive analysis of AC electrical conductivity in magnetite was performed in order to find relations between the formation of polarons,phonons and conduction by a virtual free electron gas.The analysis performed here for the first time shows experimental data for the behavior of electrons for magnetite with the scattering time shifted to the GHz region.According to our study,the DC electrical conductivity can be described by the virtual free electron gas model,and high frequency conductivity can be described by the combination of the drude model for disordered materials and Jonscher's universal power law.The observed peak at the imaginary part of AC conductivity was related to the scattering time of the electron-phonon coupling.This interaction between electrons and thermally formed phonons results in the formation of large polarons,and these are responsible for high frequency conductivity in magnetite.

关键词： Magnetite drude model Power law Electrical conductivity Virtual free electron gas

Interfacial photoconductivity effect of type-Ⅰ and type-Ⅱ Sb2Se3/Si heterojunctions for THz wave modulation

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Chinese Physics B 2023年第11期32卷 82-86页

作者：曹雪芹黄媛媛席亚妍雷珍王静刘昊楠史明坚韩涛涛张蒙恩徐新龙 Shaanxi Joint Laboratory of Graphene State Key Laboratory Incubation Base of Photoelectric Technology and Functional MaterialsInternational Collaborative Center on Photoelectric Technologyand Nano Functional MaterialsInstitute of Photonics&Photon-TechnologyNorthwest UniversityXi’an 710069China

An in-depth understanding of the photoconductivity and photocarrier density at the interface is of great significance for improving the performance of optoelectronic devices. However, extraction of the photoconductivity and photocarrier density at the heterojunction interface remains elusive. Herein, we have obtained the photoconductivity and photocarrier density of 173 nm Sb2Se3/Si(type-Ⅰ heterojunction) and 90 nm Sb2Se3/Si(type-Ⅱ heterojunction) utilizing terahertz(THz) time-domain spectroscopy(THz-TDS) and a theoretical drude model. Since type-Ⅰ heterojunctions accelerate carrier recombination and type-Ⅱ heterojunctions accelerate carrier separation, the photoconductivity and photocarrier density of the type-Ⅱ heterojunction(21.8×10^(4)S·m^(-1),1.5 × 10^(15)cm^(-3)) are higher than those of the type-Ⅰ heterojunction(11.8×10^(4)S·m^(-1),0.8×10^(15)cm^(-3)). These results demonstrate that a type-Ⅱ heterojunction is superior to a type-Ⅰ heterojunction for THz wave modulation. This work highlights THz-TDS as an effective tool for studying photoconductivity and photocarrier density at the heterojunction interface. In turn, the intriguing interfacial photoconductivity effect provides a way to improve the THz wave modulation performance.

关键词： photoconductivity Sb2 Se3/Si heterojunctions THz-TDS drude model

Radar cross section of arbitrary polished spheres at terahertz frequencies

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Journal of Systems Engineering and Electronics 2017年第6期28卷 1072-1077页

作者： Ruijun Wang Bin Deng Hongqiang Wang Yuliang Qin College of Electronic Science and Engineering National University of Defense TechnologyChangsha 410073China Uint 95876 of PLA Zhangye 734100China

We develop an efficient method for polished metallic sphere’s scattering prediction in terahertz band when its frequency dispersion property is considered. By deducing scattering solution of the lossy metallic sphere, the radar cross section(RCS)of different metallic spheres is given at terahertz frequencies. The investigation of the RCS of polished metallic spheres shows the normalized RCS is always same to the metals’ normal incidence reflectivity when the sphere becomes electrically large. The metals which have high reflectivity(such as Al, Cu, Ag and Au) show that the corresponding RCS of the spheres is almost πa2 in terahertz band. The sphere’s RCS of the transition metal such as Fe begins to decrease obviously since the far infrared.

关键词： terahertz radar cross section(RCS) sphere drude model frequency dispersion

Secrets of high thermal emission of transition metal disilicides TMSi_(2)(TM=Ta,Mo)

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Journal of Materials Science & Technology 2021年第30期89卷 114-121页

作者： Huimin Xiang Fuzhi Dai Yanchun Zhou Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials and Processing TechnologyBeijing 100076China

TMSi_(2)(TM=Ta,Mo)are extensively used as thermal emissivity agents in high emission coatings due to their well-known"high"emissivity in infrared range.However,there is a paucity of the high temperature(HT)emissivity property of these two silicides.Moreover,room temperature(RT)spectrometer measurements have demonstrated that the emittance in infrared range of two silicides was considerably low.Therefore,providing critical HT data and satisfactory elucidation on the emission incompatibility of TMSi_(2)is eagerly needed.In this contribution,combining first principles calculations and drude model,the reflectance spectra of TMSi_(2)were predicted at both RT and HT.Consistent with spectrometer measurements,the intrinsic emittance of silicides was relatively low in the entire investigated temperatures.To explain the incompatible emission behavior,two simplified models including the majority of high emissivity coating,SiO_(2),were proposed.Intriguingly,with SiO_(2)considered in simulations,no matter covered on the surface or blended in the composites,the emittance of the TMSi_(2)enhanced significantly.Our theoretical results demonstrate the non-negligible significance of oxides on the high temperature performance of silicides and provide the guidelines for improving the emission performance of silicides and searching for potential high emissivity agents.

关键词： Disilicide Optical properties Thermal emission First-principles calculations drude model

Analysis, design and simulation of MIM plasmonic filters with different geometries for technical parameters improvement

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Communications in Theoretical Physics 2020年第8期72卷 134-147页

作者： Sara Gholinezhad Shafagh Hassan Kaatuzian Mohammad Danaie Photonics Research Laboratory(PRL) Electrical Engineering DepartmentAmirkabir University of TechnologyTehranIran Electrical and Computer Engineering Faculty Semnan UniversitySemnanIran

In this paper, four optical filter topologies based on metal–insulator–metal waveguides are proposed and the designed structures are investigated numerically using finite-difference timedomain method. Triangular-shaped adjunctions have been added to the filter structures to improve their transmission spectrum. These improved structures consist of air as the insulator and silver as the metal. The relative permittivity of metal has been described via the drude,drude–Lorentz, and Palik models. The first filter’s transmission spectrum shows an acceptable transmittance. In the second optimized filter, the transmission spectrum has been improved. The transmittance spectrum can be tuned through adjusting the edge of the triangle in these four optimized filters. As a result, the bandwidths of resonance spectra can be adjusted. The theory of such tapered structures will be investigated by the tapered transmission line and will be solved with the transfer matrix method. This method shows a better performance and higher transmission efficiency in comparison with the basic structures. On the other hand, the final filter has been chosen as the best one because of its hexagonal resonator. The main reason for having a better result is due to a longer interaction length in comparison with the circular resonator. This in turn creates much better energy coupling and results in higher transmission.

关键词： plasmonics surface plasmon polariton(SPP) optical filter metal–insulator–metal(MIM)waveguide drude model