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Passively Q-switched and mode-locked Erbium-doped fiber laser with topological insulator Bismuth Selenide (Bi2Se3) as saturable absorber at C-band region
摘要： We experimentally demonstrate Q-switched and mode-locked Erbium-doped fiber laser (EDFL) by using topological insulator (TI) Bismuth Selenide (Bi2Se3) as saturable absorber (SA). The fabricated Bi2Se3 SA exhibits modulation depth and saturation intensity at 39.8% and 90.2 MW/cm2, respectively. By incorporating the fabricated Bi2Se3 SA into the laser cavity, Q-switching operation is generated with repetition rate ranging from 23.5 kHz to 68.2 kHz, pulse width ranging from 2.4 μs to 8.6 μs and maximum peak power is calculated at 19.9 mW. Our cavity can also generate soliton mode-locked pulse with repetition rate of 23.3 MHz and pulse width of 0.63 ps by inserting an additional 5 m long single mode fiber (SMF) into the existing laser cavity. Spectral peaks due to Kelly side-bands and four wave mixing (FWM) were observed on the soliton spectrum. Both Q-switching and mode-locking pulses are stable in the laboratory environment, allowing the realization of compact and low cost pulsed fiber laser with Bi2Se3 SA for various photonics applications.
关键词： Topological insulator,Bismuth-selenide,Q-switched,EDFL,Mode-locked
更新于2025-11-28 14:24:03
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Bi2Te3 Topological Insulator for Domain-Wall Dark Pulse Generation from Thulium-Doped Fiber Laser
摘要： We have experimentally demonstrated domain-wall (DW) dark pulses from a thulium-doped fiber laser incorporating a topological insulator saturable absorber (SA). The bulk-structured Bi2Te3 was used as the SA, which was constructed on a fiber ferrule platform through the deposition of the Bi2Te3 mixed with distilled water. The DW dark pulses were generated from the thulium-doped fiber laser cavity with a dual wavelength at 1956 nm and 1958 nm. The dark pulse width and the repetition rate were measured as ~10.3 ns and ~20.7 MHz over the pump power of ~80 mW, respectively. To the best of our knowledge, this work is the first demonstrated generation of the DW dark pulse from a thulium-doped fiber laser using nanomaterial-based SA.
关键词： fiber lasers,Bi2Te3,topological insulator,domain-wall dark pulses
更新于2025-11-28 14:23:57
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Realization of a three-dimensional photonic topological insulator
摘要： Confining photons in a finite volume is highly desirable in modern photonic devices, such as waveguides, lasers and cavities. Decades ago, this motivated the study and application of photonic crystals, which have a photonic bandgap that forbids light propagation in all directions1–3. Recently, inspired by the discoveries of topological insulators4,5, the confinement of photons with topological protection has been demonstrated in two-dimensional (2D) photonic structures known as photonic topological insulators6–8, with promising applications in topological lasers9,10 and robust optical delay lines11. However, a fully three-dimensional (3D) topological photonic bandgap has not been achieved. Here we experimentally demonstrate a 3D photonic topological insulator with an extremely wide (more than 25 per cent bandwidth) 3D topological bandgap. The composite material (metallic patterns on printed circuit boards) consists of split-ring resonators (classical electromagnetic artificial atoms) with strong magneto-electric coupling and behaves like a ‘weak’ topological insulator (that is, with an even number of surface Dirac cones), or a stack of 2D quantum spin Hall insulators. Using direct field measurements, we map out both the gapped bulk band structure and the Dirac-like dispersion of the photonic surface states, and demonstrate robust photonic propagation along a non-planar surface. Our work extends the family of 3D topological insulators from fermions to bosons and paves the way for applications in topological photonic cavities, circuits and lasers in 3D geometries.
关键词： 3D photonic topological insulator,split-ring resonators,Dirac surface states,robust photonic propagation,topological bandgap
更新于2025-09-23 15:23:52
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<sup>125</sup> Te nuclear magnetic resonance and impedance spectroscopy study of topological insulator Bi <sub/>2</sub> Te <sub/>3</sub> nanoparticles mixed with insulating Al <sub/>2</sub> O <sub/>3</sub> nanoparticles
摘要： We have studied topological insulator Bi2Te3 nanoparticles mixed with insulating Al2O3 nanoparticles by means of 125Te nuclear magnetic resonance (NMR) and impedance spectroscopy. Our 125Te NMR lineshape measurements revealed the Knight shift of a satellite peak that increased with the mixing ratio of the Al2O3 nanoparticles, indicating that the mixing increases the surface-to-volume ratio of the Bi2Te3 nanoparticles. It is also shown that the impedance spectroscopy can be employed as a simple and effective means of distinguishing the surface electrical properties of the topological insulators in general.
关键词： surface electrical properties,topological insulator Bi2Te3 nanoparticles,125Te nuclear magnetic resonance,impedance spectroscopy
更新于2025-09-23 15:23:52
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Structural and vibrational properties of PVT grown BiTeCl microcrystals
摘要： High-quality BiTeCl microcrystals are grown by the physical vapor transport (PVT) method without using a foreign transport agent. The plate-like microcrystals with a developed (0001) surface are up to ~500 μm in diameter. The grown crystal phase composition was identified by the X-ray single crystal structure analysis in space group P63mc: a = 4.2475(6) ?, c = 12.409(2) ?, Z = 2 (R = 0.0343). The BiTeCl microcrystal phase purity was verified by Raman microspectrometry under excitation at λ = 632.8 and 532.1 nm.
关键词： PVT crystal growth,crystal structure,topological insulator,SEM,BiTeCl,Raman spectroscopy
更新于2025-09-23 15:23:52
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Two dimensional topological insulators in bilayer BiB
摘要： With the help of ?rst-principles calculations, we propose a new type of two dimensional (2D) topological insulator BiB with bilayer hexagonal lattice. Its dynamic stability was con?rmed by the phonon spectrum. When spin-orbit coupling (SOC) e?ect is not considered, the low energy electronic states around the Fermi level show metallic characteristics. However, the SOC will induce a global band gap and turn this 2D material into topological insulators with nontrivial edge states. Surprisingly, two mechanisms, including crystal ?eld and strong SOC, induce two band inversions and manipulate the low energy electronic states simultaneously. The BiB provides a fertile platform for studying the interactions between the two di?erent mechanisms in the same topological insulator. Moreover, the sizable global nontrivial band gap indicates its high working temperature.
关键词： Topological insulator,Edge states,Z2,Spin-orbit coupling (SOC)
更新于2025-09-23 15:22:29
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Growth and physical properties of Ce(O,F)Sb(S,Se)2 single crystals with site-selected chalcogen atoms
摘要： Ce(O,F)Sb(S,Se)2 single crystals were successfully grown using a CsCl/KCl ?ux method. The obtained crystals have a plate-like shape with the typical size of 1–2 mm and well-developed ab-plane, which enables X-ray single crystal structural analysis. The Ce(O,F)Sb(S,Se)2 crystallizes in a monoclinic space group, P21/m, with lattice parameters of a = 4.121(7) ?, b = 4.109(7) ?, c = 13.233(15) ?, β = 97.94(7) °. It is composed of alternate stacking of Ce-(O,F) and Sb-SSe layers, and the Sb-SSe layer includes selective occupation of Se atoms in its in-plane site. The valence state of Ce is estimated to be Ce3+ by X-ray absorption ?ne spectroscopy analysis. The single crystals show an insulating behavior, and a magnetic ordering around 6 K.
关键词： E. Photoemission spectroscopy,B. Flux growth,D. Topological insulator,A. Layered mixed-anion compounds
更新于2025-09-23 15:22:29
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Berry phase in strained InSb whiskers
摘要： Strain influence on the longitudinal magnetoresistance for the n-type conductivity InSb whiskers doped by Sn to concentrations 6·1016–6·1017 сm–3 were studied at temperatures from 4.2 to 50 K and magnetic field up to 10 T. The Shubnikov–de Haas oscillations at low temperatures were revealed in the strained and unstrained samples with all range doping concentration. Some peaks of the longitudinal magnetoresistance split as a doublet in the InSb whiskers with doping concentration in the vicinity to metal-insulator transition. Taking into account peak splitting giant g-factor from 30 to 60 was defined for strained and unstrained samples. The magnetoresistance oscillation period of the InSb whiskers doesn’t differ under strain for all doping concentration, but Fermi energy increases and electron effective mass mс decreases and consists 0.02 m0. Berry phase presence was also revealed in strained n-InSb whiskers that shows their transition under a strain to topological insulator phase.
关键词： Berry phase,topological insulator,strained InSb whiskers,Shubnikov–de Haas oscillations,magnetoresistance
更新于2025-09-23 15:21:21
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Numerical analysis of surface and edge states in slabs, stripes, rods and surface steps of topological insulators
摘要： By numerically solving the e?ective continuous model of a topological insulator with parameters corresponding to the band structure of the topological insulator Bi2Se3, we analyze possible appearance of one-dimensional states in various geometries. Massless Dirac fermions are found at the edges of thin ribbons with surface oriented not only along the van der Waals gap but also in the perpendicular direction. Thick rods and slabs with surface steps host massive modes localized on surface faces. We argue that the modes are massive and their origin is due to the di?erence in the Dirac point energy of adjacent faces. The absence of one-dimensional states near edges of a large rectangular rod and surface steps is demonstrated.
关键词： bound state,topological insulator,edge states,surface step
更新于2025-09-23 15:21:21
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Transport in a thin topological insulator with potential and magnetic barriers
摘要： We study transport across either a potential or a magnetic barrier which is placed on the top surface of a three-dimensional thin topological insulator (TI). For such thin TIs, the top and bottom surfaces interact via a coupling λ which influences the transport properties of junctions constructed out of them. We find that for junctions hosting a potential barrier, the differential conductance oscillates with the barrier strength. The period of these oscillations doubles as the coupling λ changes from small values to a value close to the energy of the incident electrons. In contrast, for junctions with a magnetic barrier, the conductance approaches a nonzero constant as the barrier strength is increased. This feature is in contrast to the case of transport across a single TI surface where the conductance approaches zero as the strength of a magnetic barrier is increased. We also study the spin currents for these two kinds of barriers; in both cases, the spin current is found to have opposite signs on the top and bottom surfaces. Thus this system can be used to split applied charge currents to spin currents with opposite spin orientations which can be collected by applying opposite spin-polarized leads to the two surfaces. We show that several of these features of transport across finite width barriers can be understood analytically by studying the δ-function barrier limit. We discuss experiments which may test our theory.
关键词： magnetic barrier,transport,spin current,potential barrier,topological insulator
更新于2025-09-23 15:21:01