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Controlling Topological States in Topological/Normal Insulator Heterostructures
摘要： We have performed a systematic investigation of the nature of the nontrivial interface states in topological/normal insulator (TI/NI) heterostructures. On the basis of first principles and a recently developed scheme to construct ab initio effective Hamiltonian matrices from density functional theory calculations, we studied systems of realistic sizes with high accuracy and control over the relevant parameters such as TI and NI band alignment, NI gap, and spin?orbit coupling strength. Our results for IV?VI compounds show the interface gap tunability by appropriately controlling the NI thickness, which can be explored for device design. Also, we verified the preservation of an in-plane spin texture in the interface-gaped topological states.
关键词： density functional theory,heterostructures,spin?orbit coupling,topological insulators,normal insulators
更新于2025-09-23 15:21:21
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Electronic and Topological Properties of Silicene, Germanene and Stanene
摘要： In this chapter, we review the recent progress on electronic and topological properties of monolayer topological insulators including silicene, germanene and stanene. We start with the description of the topological nature of the general Dirac system and then apply it to silicene by introducing the spin and valley degrees of freedom. Based on them, we classify all topological insulators in the general honeycomb system. We discuss topological electronics based on honeycomb systems. We introduce the topological Kirchhoff law, which is a conservation law of topological edge states. Field effect topological transistor is proposed based on the topological edge states. We show that the conductance is quantized even in the presence of random distributed impurities. Monolayer topological insulators will be a key for future topological electronics and spin-valleytronics.
关键词： topological Kirchhoff law,silicene,topological insulators,topological electronics,Dirac system,field effect topological transistor,spin and valley degrees of freedom,stanene,quantized conductance,germanene
更新于2025-09-23 15:21:21
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Mode-Locked Topological Insulator Laser Utilizing Synthetic Dimensions
摘要： We propose a system that exploits the fundamental features of topological photonics and synthetic dimensions to force many semiconductor laser resonators to synchronize, mutually lock, and under suitable modulation emit a train of transform-limited mode-locked pulses. These lasers exploit the Floquet topological edge states in a 1D array of ring resonators, which corresponds to a 2D topological system with one spatial dimension and one synthetic frequency dimension. We show that the lasing state of the multielement laser system possesses the distinct characteristics of spatial topological edge states while exhibiting topologically protected transport. The topological synthetic-space edge mode imposes a constant-phase difference between the multifrequency modes on the edges, and together with modulation of the individual elements forces the ensemble of resonators to mode lock and emit short pulses, robust to disorder in the multiresonator system. Our results offer a proof-of-concept mechanism to actively mode lock a laser diode array of many lasing elements, which is otherwise extremely difficult due to the presence of many spatial modes of the array. The topological synthetic-space concepts proposed here offer an avenue to overcome this major technological challenge and open new opportunities in laser physics.
关键词： Synthetic Dimensions,Topological Insulators,Mode-Locked Lasers,Photonics
更新于2025-09-23 15:21:01
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THz photodetector using sideband-modulated transport through surface states of a 3D topological insulator
摘要： The transport properties of the surface charge carriers of a three dimensional topological insulator under a terahertz (THz) field along with a resonant double barrier structure is theoretically analyzed within the framework of Floquet theory to explore the possibility of using such a device for photodetection purposes. We show that due to the contribution of elastic and inelastic scattering processes in the resulting transmission, side-bands are formed in the conductance spectrum. This side band formation is similar to the side-bands formation in cavity transmission spectra in an optical cavity and this information can be used to detect the frequency of unknown THz radiation. The dependence of the conductance on the bias voltage, the effect of THz radiation on resonances and the influence of zero energy points on the transmission spectrum are also discussed.
关键词： THz radiation,Floquet theory,surface states of topological insulators,side bands in transmission spectrum
更新于2025-09-23 15:21:01
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Solar-driven interfacial evaporation
摘要： As a ubiquitous solar-thermal energy conversion process, solar-driven evaporation has attracted tremendous research attention owing to its high conversion efficiency of solar energy and transformative industrial potential. In recent years, solar-driven interfacial evaporation by localization of solar-thermal energy conversion to the air/liquid interface has been proposed as a promising alternative to conventional bulk heating-based evaporation, potentially reducing thermal losses and improving energy conversion efficiency. In this Review, we discuss the development of the key components for achieving high-performance evaporation, including solar absorbers, evaporation structures, thermal insulators and thermal concentrators, and discuss how they improve the performance of the solar-driven interfacial evaporation system. We describe the possibilities for applying this efficient solar-driven interfacial evaporation process for energy conversion applications. The exciting opportunities and challenges in both fundamental research and practical implementation of the solar-driven interfacial evaporation process are also discussed.
关键词： energy conversion,thermal insulators,thermal concentrators,solar absorbers,evaporation structures,interfacial evaporation,solar-driven evaporation,solar-thermal energy conversion
更新于2025-09-23 15:21:01
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Analysis of Salt Mixture Contamination on Insulators via Laser-Induced Breakdown Spectroscopy
摘要： The composition of contamination deposited on transmission line insulators can affect their surface flashover voltage. Currently, there is no rapid on-line method to detect this contamination composition in power grids. In this paper, we applied laser-induced breakdown spectroscopy (LIBS) to analyze contamination on insulator surfaces. Usually, Na and Ca salts are found in contamination along with various sulfate, carbonate, and chloride compounds. As an element’s detection method, LIBS can only measure a certain element content, for example, Ca. The mixture of various compounds with the same cations can influence the LIBS signal. The influence of mixing ratios on the calibration curves and relative spectral intensity was studied via LIBS. Na2CO3, NaHCO3, CaSO4, and CaCO3 samples containing different proportions of Na and Ca were prepared. The linear correlation coefficients (R2) for the Na and Ca calibration curves generated using various mixing ratios were analyzed. The results showed that the mixture ratio did not dramatically affect the linear calibration curves for mixtures containing the same cations. This finding may significantly reduce the difficulty of applying LIBS analysis for complex contamination on insulators. The laser energy density had effects on the spectral characteristics of the measured elements. The partial least-square regression (PLSR) model can improve the accuracy of Na and Ca prediction.
关键词： salt,insulators,calibration curves,laser-induced breakdown spectroscopy,contamination
更新于2025-09-23 15:21:01
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Resonant pumping of polaritonic SSH chains
摘要： An optical-lattice realization of a Su-Schrieffer-Heeger chain is theoretically investigated. The topological state is controlled by the relative phase of the lasers constructing the lattice. The hopping amplitudes are calculated within the harmonic approximation to the optical potential in the vicinity of its minima. Finally, we examine polaritons loaded into adiabatically shaken optical lattices with damping and pumping and demonstrate that, in the case of resonant pumping, the system manifests different quantitative and qualitative behaviour for topologically trivial and non-trivial phases.
关键词： Su-Schrieffer-Heeger chain,topological insulators,polaritons,resonant pumping,optical lattices
更新于2025-09-23 15:21:01
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Transmission-Line Model for Materials with Spin-Momentum Locking
摘要： We provide a transmission-line representation for channels exhibiting spin-momentum locking (SML) that can be used for both time-dependent and steady-state transport analysis on a wide variety of materials with spin-orbit coupling such as topological insulators, Kondo insulators, transition metals, semimetals, oxide interfaces, and narrow band-gap semiconductors. This model is based on a time-dependent four-component di?usion equation obtained from the Boltzmann transport equation assuming linear response and elastic scattering in the channel. We classify all electronic states in the channel into four groups (U+, D+, U?, and D?) depending on the spin index [up (U), down (D)] and the sign of the x component of the group velocity (+, ?) and assign an average electrochemical potential to each of the four groups to obtain the four-component di?usion equation. For normal metal channels, the model decouples into the well-known transmission-line model for charge and a time-dependent version of the Valet-Fert equation for spin. We ?rst show that, in the steady-state limit, our model leads to simple expressions for charge-spin interconversion in SML channels in good agreement with existing experimental data on diverse materials. We then use the full time-dependent model to study spin-charge separation in the presence of SML, a subject that has been controversial in the past. Our model shows that the charge and spin signals travel with two distinct velocities, resulting in well-known spin-charge separation, which is expected to persist even in the presence of SML. However, our model predicts that the lower velocity signal is purely spin, while the higher velocity signal is largely charge with an additional spin component proportional to the degree of SML, which has not been noted before. Finally, we note that our model can be used within standard circuit simulators such as SPICE to obtain numerical results for complex geometries.
关键词： spin-orbit coupling,spin-charge separation,transmission-line model,topological insulators,charge-spin interconversion,spin-momentum locking
更新于2025-09-23 15:21:01
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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) - Theoretical Analysis of a Non-Quantized Square-Root Topological Insulator using Photonic Aharonov-Bohm Cages
摘要： Topological insulators have to date seen a variety of manifestations. All available realizations of topological insulators, however, share a common feature: their spectral bands are attributed with a nonlocal topological index that is quantized. In this work, we report a new type of insulator exhibiting spectral bands with nonquantized indices, yet robust boundary states. We provide a theoretical analysis based on the quantization of the indices in the corresponding system where the square of the Hamiltonian is taken and exemplify the general paradigm using photonic Aharonov-Bohm cages. Taking the square-root of the Klein-Gordon Hamiltonian has opened up an entirely new realm of physics: the resulting Dirac operator provided a relativistic quantum description of massive spin-1/2 fermionic particles, thus disclosing the fine-structure spectra of atoms or the anomalous Zeeman effect. Along a similar line, we consider a three-band model that can have nonquantized topological indices, but with a spectral symmetry that gives rise to quantized topological invariants when the square of the Hamiltonian is taken. This relation generates the topological characterization of the square-root model and allows us to establish a topological bulk-boundary correspondence with states that can be used as in-gap, protected and controllable qubits. Notably, whereas taking the square of the Dirac operator leads to the topologically trivial Klein-Gordon model, in our case, the squared model maps to an effective Su-Schrieffer-Heeger (SSH) model in its nontrivial phase. Optical settings prove to be ideally suited for realizing various topological phenomena. In this vein, we employ photonic waveguide lattices with effective negative hopping amplitudes to realize a 3-band quasi-1D chain made of photonic Aharonov-Bohm cages that exemplifies our general description. In summary, we predict and demonstrate the physics of a square-root topological insulator, using a photonic platform. Specifically, we show that the AB cages have in-gap states, above bands possessing nonquantized Zak’s phases. Furthermore, we find that these states are robust, both in energy and localization, against symmetry-preserving perturbation and disorder. We show that this robustness stems from the corresponding system where the square of the Hamiltonian is taken and where the bands exhibit quantized topological indices with associated in-gap boundary states.
关键词： nonquantized indices,photonic Aharonov-Bohm cages,square-root topological insulator,robust boundary states,Topological insulators
更新于2025-09-23 15:19:57
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Influence of an Insulator Layer on the Charge Transport in a Metal/Insulator/n-AlGaN Structure
摘要： In this work, a parametric study revealing the impact of metal-insulator-semiconductor (MIS) structure in improving the electron injection between the n-AlGaN layer and the electrode metal is conducted. After inserting an insulator at the surface between the n-AlGaN layer and the electrode metal, the energy band bending of the thin insulator manipulates the conduction band barrier height between the electrode and the n-AlGaN layer, which enables the electrons to more efficiently tunnel through the thin insulator barrier. As a result, the electrical characteristics for the devices are significantly improved if the MIS structure is optimized. Furthermore, the impact of the affinity, the relative dielectric constant, and the bandgap for the insulator on the electron injection is investigated. Meanwhile, it is found that the electron injection is sensitive to the thickness and the length for the insulator. Detailed analysis regarding the electron transport and the device physics are reported in this work.
关键词： insulators,semiconductors,electrical characteristics,electron transport,n-AlGaN
更新于2025-09-19 17:15:36