Search

Topological antiferromagnets have a significant role to play in the modern day electronics and spintronics due to the presence of peculiar symmetries and magnetically driven large anomalous transport behaviour. We report the observation of anomalous Hall effect in Mn3Sn polycrystalline thin films deposited on Al2O3 substrate with a large anomalous Hall conductivity of 65 (Ωcm)−1 at 3 K. The Hall and magnetic measurements show a very small hysteresis owing to a weak ferromagnetic moment present in this material. The longitudinal resistivity decreases sufficiently for the thin films as compared to the polycrystalline bulk sample used as the target for the film deposition. The anomalous Hall resistivity and conductivity decreases almost linearly with the increase in the temperature. A negative magnetoresistance is observed for all the measured temperatures with the negative decrease in the magnitude with the increase in temperature.

Topological insulators (TI), as a kind of fantastic nanomaterial with excellent electrical and optical properties, have attracted particular attention due to the promising applications in optoelectronic devices. Herein, we experimentally demonstrated the interaction between light and molybdenum disulfide (MoS2) monolayer with an antimony telluride (Sb2Te3) TI nanoparticle. It was found that photoluminescence (PL) emission and Raman scattering signal can be boosted by 5 and 8 folds in MoS2 monolayer integrated with the TI nanoparticle, respectively. The measured and simulated dark-field scattering spectra illustrated that the enhancement of light–matter interaction could be derived from the generation of localized surface plasmons on the TI nanoparticle with distinctly boosted electric field. We also found that there exists a redshift of 5 nm for the enhanced PL peak, which could be attributed to the formation of trions in MoS2 induced by plasmon doping. This work would provide a new pathway for the applications of TI nanoparticles in the optoelectronics, especially light–matter interaction enhancement.

The rapid development of neuromorphic computing has stimulated extensive research interest in artificial synapses. Optoelectronic artificial synapses using laser beams as stimulus signals have the advantages of broadband, fast response, and low crosstalk. However, the optoelectronic synapses usually exhibit short memory duration due to the low lifetime of the photo-generated carriers. It greatly limits the mimicking of human perceptual learning, which is a common phenomenon in sensory interactions with the environment and practices of specific sensory tasks. Herein, a heterostructure optoelectronic synapse based on graphene nanowalls and CsPbBr3 quantum dots was fabricated. The graphene/CsPbBr3 heterojunction and the natural middle energy band in graphene nanowalls extend the carrier lifetime. Therefore, a long half-life period of photocurrent decay - 35.59 s has been achieved. Moreover, the long-term optoelectronic response can be controlled by the adjustment of numbers, powers, wavelengths, and frequencies of the laser pulses. Next, an artificial neural network consisting of a 28 × 28 synaptic array was established. It can be used to mimic a typical characteristic of human perceptual learning that the ability of sensory systems is enhanced through a learning experience. The learning behavior of image recognition can be tuned based on the photocurrent response control. The accuracy of image recognition keeps above 80% even under a low-frequency learning process. We also verify that less time is required to regain the lost sensory ability that has been previously learned. This approach paves the way toward high-performance intelligent devices with controllable learning of visual perception.

We report the existence of ferromagnetism in the thiospinel compound CuCo2S4 with Tc ∼ 125 K. The magneto-electronic transport of the CuCo2S4 demonstrates a metallic conductivity and positive magnetoresistance at high temperature. At low temperature, in the ferromagnetic state, there is evidence of spin-transport coupling with magnetic domains giving a region of negative magnetoresistance near the coercive field. The electronic band structure of CuCo2S4 was calculated using density-functional theory (DFT), which shows a ferromagnetic metallic state, in agreement with experiment. With nickel doping, both the spinel CuCo1.5Ni0.5S4 and CuCoNiS4 display paramagnetism down to the lowest measured temperature (3 K). This indicates that, as in other itinerant magnetic sulfides, the exchange interactions are highly sensitive to electron/hole doping. The tunable magnetism in the spinel CuCo2S4, together with its high conductivity, suggests that this thiospinel material could be a candidate for spintronic applications.

Three-dimensional (3D) topological semimetals (TSMs) are a new class of Dirac materials that can be viewed as 3D graphene and are referred to as Dirac semimetals (DSMs) or Weyl semimetals (WSMs) depending on whether time reversal symmetry and/or inversion symmetry are protected, respectively. Despite some interesting results on Dirac- to Weyl-semimetal phase transitions under conditions of low temperature or strong magnetic field (B), all of them are reversible phenomena. Here, we report for the first time a possible permanent transition in a single TSM by ion implantation. A Dirac- to Weyl-semimetal phase transition in a Bi0.96Sb0.04 DSM results from inversion-symmetry breaking induced by implantation with nonmagnetic Au ions for implant fluences (ϕG) ≥ 3.2 × 1016 Au cm−2. This phenomenon is evidenced by the ϕG-dependent behavior of the Raman spectra and quantum-oscillation parameters extracted from magnetoresistance (MR) measurements, which show abrupt changes at ϕG ≥ 3.2 × 1016 Au cm−2. The verification of the transition is further supported by observations of negative MR in the longitudinal B // electric field orientation, indicating the existence of a chiral anomaly in Weyl fermions induced by implantation with nonmagnetic Au ions. In contrast, implantation with magnetic Mn ions exhibits no such particular behavior. Our findings demonstrate the first realization of a possible permanent DSM-to-WSM phase transition in a single material by the simple approach of implantation using nonmagnetic elements.

Topological insulators (TIs) are emergent materials with unique band structure, which allow the study of quantum effect in solids, as well as contribute to high-performance quantum devices. To achieve the better performance of TIs, here, we present a codoping strategy using synergistic rare-earth (RE) Sm and transition-metal Fe dopants in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ single crystals, which combine the advantages of both a transition-metal-doped TI [high ferromagnetic ordering temperature and observed quantum anomalous Hall effect (QAHE)], and a RE doped TI (large magnetic moments and significant spin-orbit coupling). In the as-grown single crystals, clear evidences of ferromagnetic ordering were observed. The angle-resolve photoemission spectroscopy indicates the ferromagnetism opens a \ensuremath{\sim}44 meV band gap at the surface Dirac point. Moreover, the mobility of the carriers at 3 K is $\ensuremath{\sim}7400\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}/\mathrm{Vs}$, and we thus observed an ultra-strong Shubnikov--de Haas oscillation in the longitudinal resistivity, as well as the Hall steps in transverse resistivity 14 T. Our transport and angular-resolved photoemission spectroscopy results suggest that the RE and transition metal codoping in the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ system is a promising avenue to implement the QAHE, as well as harnessing the massive Dirac fermion in electrical devices.

As personal electronic devices increasingly rely on cloud computing for energy-intensive calculations, the power consumption associated with the information revolution is rapidly becoming an important environmental issue. Several approaches have been proposed to construct electronic devices with low-energy consumption. Among these, the low-dissipation surface states of topological insulators (TIs) are widely employed. To develop TI-based devices, a key factor is the maximum temperature at which the Dirac surface states dominate the transport behavior. Here, we employ Shubnikov-de Haas oscillations (SdH) as a means to study the surface state survival temperature in a high-quality vanadium doped Bi1.08Sn0.02Sb0.9Te2S single crystal system. The temperature and angle dependence of the SdH show that: (1) crystals with different vanadium (V) doping levels are insulating in the 3–300 K region; (2) the SdH oscillations show two-dimensional behavior, indicating that the oscillations arise from the pure surface states; and (3) at 50 K, the V0.04 single crystals (Vx:Bi1.08-xSn0.02Sb0.9Te2S, where x = 0.04) still show clear sign of SdH oscillations, which demonstrate that the surface dominant transport behavior can survive above 50 K. The robust surface states in our V doped single crystal systems provide an ideal platform to study the Dirac fermions and their interaction with other materials above 50 K.

In the 1960s, it was proposed that in small indirect band-gap materials, excitons can spontaneously form because the density of carriers is too low to screen the attractive Coulomb interaction between electrons and holes. The result is a novel strongly interacting insulating phase known as an excitonic insulator. Here we employ scanning tunnelling microscopy (STM) and spectroscopy (STS) to show that the enhanced Coulomb interaction in quantum-confined elemental Sb nanoflakes drives the system to the excitonic insulator state. The unique feature of the excitonic insulator, a charge density wave (CDW) without periodic lattice distortion, is directly observed. Furthermore, STS shows a gap induced by the CDW near the Fermi surface. Our observations suggest that the Sb(110) nanoflake is an excitonic insulator.

Exploring highly efficient photocatalysts is an urgent task for achieving efficient solar-to-chemical conversion. Plasmonic effect is widely used in improving the photocatalytic properties via reducing the activation barrier for chemical reactions, enhancing the absorption of the photocatalysts or injecting the hot carriers into the photocatalysts from the plasmon metals. In this work, we design BiOCl-Ag-E with Ag loaded on the edge side of BiOCl. This hybrid structure takes the advantages of highly photocatalytic active (001) facet of BiOCl and the plasmonic effect. The plasmon metal is proposed to provide the (001) facets with more photogenerated charge carriers driving by the internal electric field, which is convinced by the photocurrent response and the detection of active species. Due to the accumulation of more negative charge carriers on (001) facet, BiOCl-Ag-E presents outstanding waste-water cleaning and CO2 photoreduction properties. The methodology of material design in this work paves the way for future design of efficient photocatalysts.

Topological insulators as new emerging building blocks in electronics and photonics present promising prospects for exciting surface plasmons and enhancing light–matter interaction. Thus, exploring the visible-range plasmonic response of topological insulators is significant to reveal their optical characteristics and broaden their applications at high frequencies. Herein, we report the experimental demonstration of a visible-range surface plasmon resonance (SPR) effect on an antimony telluride (Sb2Te3) topological insulator film. The results show that the SPR can be excited with a relatively small incident angle in the Kretschmann configuration based on the Sb2Te3 film. Especially, we develop an impactful digital holographic imaging system based on the topological insulator SPR and realize the dynamic monitoring of refractive index variation. Compared with the traditional SPR, the Sb2Te3-based SPR possesses a broader measurement range. Our findings open a new avenue for exploring the optical physics and practical applications of topological insulators, such as environmental and biochemical sensing.

Magnetic resonances not only play crucial roles in artificial magnetic materials but also offer a promising way for light control and interaction with matter. Recently, magnetic resonance effects have attracted special attention in plasmonic systems for overcoming magnetic response saturation at high frequencies and realizing high-performance optical functionalities. As novel states of matter, topological insulators (TIs) present topologically protected conducting surfaces and insulating bulks in a broad optical range, providing new building blocks for plasmonics. However, until now, high-frequency (e.g. visible range) magnetic resonances and related applications have not been demonstrated in TI systems. Herein, we report for the first time, to our knowledge, a kind of visible range magnetic plasmon resonances (MPRs) in TI structures composed of nanofabricated Sb2Te3 nanogrooves. The experimental results show that the MPR response can be tailored by adjusting the nanogroove height, width, and pitch, which agrees well with the simulations and theoretical calculations. Moreover, we innovatively integrated monolayer MoS2 onto a TI nanostructure and observed strongly reinforced light–MoS2 interactions induced by a significant MPR-induced electric field enhancement, remarkable compared with TI-based electric plasmon resonances (EPRs). The MoS2 photoluminescence can be flexibly tuned by controlling the incident light polarization. These results enrich TI optical physics and applications in highly efficient optical functionalities as well as artificial magnetic materials at high frequencies., Topological insulators: visible range magnetic resonances Nanostructured antimony telluride (Sb2Te3) can support visible range magnetic resonances and dramatically enhance the weak interactions of light with 2D materials. Hua Lu and workers from China and Australia used focused ion beam milling to write a grating of periodic nanogrooves into single-crystalline Sb2Te3, a well-known topological insulator. They then placed a flake of the 2D material MoS2 on top. Characterization showed the existence of a kind of magnetic plasmon resonances (MPRs) with a resonant wavelength that redshifts with increasing nanogroove height and pitch and blueshifts with increasing nanogroove width. Visible photoluminescence experiments showed that the MPRs can dramatically increase the emission from the MoS2, which could be tuned by changing the polarization angle of the incident excitation light. The findings are expected to aid the development of nanoscale optical devices made from layered nanomaterials.

Thermoelectric (TE) materials have attracted extensive interest because of their ability to achieve direct heat-to-electricity conversion. They provide an appealing renewable energy source in a variety of applications by harvesting waste heat. The record-breaking figure of merit reported for single crystal SnSe has stimulated related research on its polycrystalline counterpart. Boosting the TE conversion efficiency requires increases in the power factor and decreases in thermal conductivity. It is still a big challenge, however, to optimize these parameters independently because of their complex interrelationships. Herein, we propose an innovative approach to decouple electrical and thermal transport by incorporating carbon fiber (CF) into polycrystalline SnSe. We show that the incorporation of highly conductive CF can successfully enhance the electrical conductivity, while greatly reducing the thermal conductivity of polycrystalline SnSe. As a result, a high TE figure-of-merit (zT) of 1.3 at 823 K is obtained in p-type SnSe/CF composite polycrystalline materials. Furthermore, SnSe samples incorporated with CFs exhibit superior mechanical properties, which are favorable for device fabrication applications. Our results indicate that the dispersion of CF can be a good way to greatly improve both TE and mechanical performance.

Polymer-based nanocomposites with hybrid fillers are expected to possess high energy storage density taking advantage of different morphologies and electric properties of the nanofillers. In this article, hybrid semi-conductive nanofillers with MoS2 two-dimensional (2-D) nanosheets and ZnO zero-dimensional (0-D) nanoparticles in different ratios were fabricated by the wet chemical route and ultrasonic mixing. The ZnO nanoparticles have a good distribution on MoS2 nanosheets confirmed by TEM, XRD, and XPS results. The P(VDF-CTFE-DB)/ZnO@MoS2 composites with different weight percent of fillers were prepared by solution cast, and the influence of hybrid fillers on polymer matrix was systematically investigated. P(VDF-CTFE-DB) with hybrid filler exhibits optimized discharged energy density of 7.2 J/cm3 and efficiency of 83% at 300 MV/m, both of which are higher than those reported in polymer nanocomposites at the same electric field. Moreover, the distribution of polarization and electric field of the distribution of 2D fillers in four different models for composite P(VDF-CE-DB)/ZnO@MoS2 with 2 mol% of fillers were investigated by the finite element simulation analysis (COMSOL). In addition, the nanocomposite also possesses high power density and excellent fatigue reliability, demonstrating it can be a good candidate for energy storage device that requires high energy density at a low electric field for safer working conditions.

The magnetic exchange bias (EB) effect is one of the representative interlayer magnetic coupling phenomena and is widely utilized in numerous technological applications. However, its mechanism is still elusive even in a simple magnetic bilayered system because of the complex interface magnetic orders. Van der Waals (vdW) layered magnetic materials may provide an essential platform for deeply understanding the detailed mechanism of the EB owing to its ideal interface structure. Here we first observed the positive exchange-biased anomalous Hall effect with a hopping switching behavior in the FeGeTe vdW nano-flakes. After systemically studying the cooling field dependence properties of the EB effect, we propose that the coexistence of stable and frustrated surface magnetization of the antiferromagnetic (AFM) phase will modify the total interface coupling energy density between the ferromagnetic and AFM phases. This model could provide a consistent description for such unusual EB effect based on microspin simulation.

Zone-melted Bi2Te2.7Se0.3 (ZM BTS) alloys are typical n-type commercial thermoelectric (TE) materials and are utilized for refrigeration and power generation near room temperature. They usually suffer from poor mechanical performance, as well as having a low figure of merit (ZT). In this work, we report an effective composite strategy to improve both the TE and mechanical performance of n-type BTS materials by incorporating carbon microfibers. The introduction of carbon microfibers in BTS effectively reduces the lattice thermal conductivity due to phonon scattering at multi-scale boundaries and due to the large interfacial thermal resistance arising from phonon mismatch between the constituent phases. Simultaneously, it also gives rise to an enhancement of the electrical conductivity, which originates from the increased carrier density without significant limitation on its weighted mobility. Consequently, a high peak ZT of 1.1 at 400 K and an average ZTave value of 0.95 are achieved in the temperature range 300 ~ 550 K, yielding a calculated efficiency of η = 9%. Moreover, the BTS/carbon microfiber composites show superior compressive strength compared to a commercial ZM BTS sample. This improved strength is highly desirable for real-world TE applications. Our results demonstrate a novel way to produce high-performance TE materials, in which interfaces with large thermal resistance are used to achieve low thermal conductivity without significantly degrading the electrical properties of the materials.

As a new class of nanomaterials, topological insulators with the Dirac surface conducting state and insulating bulk state offer a promising platform for plasmonics with breaking through the frequency and integration limitation of traditional materials. The combination of topological insulators with atomic-layer materials will be significant for the realization of integrated plasmonic functional devices. Herein, we experimentally report the plasmon-enhanced photoluminescence (PL) emission behavior of molybdenum disulfide (MoS2) single layer integrated with an antimony telluride (Sb2Te3) topological insulator nanogap. It is found that the PL response of MoS2 on the nanogap is dependent on the polarization of incident light. The MoS2 PL intensity can be distinctly improved with plasmonic excitation on Sb2Te3 nanogap. These results will contribute to exploring plasmonic behaviors of topological insulators and their applications in enhanced light-matter interaction for nanoscale light emission and harvesting devices.

Topological Weyl semimetals are a new class of quantum materials with 3D Dirac electronic states. A variety of novel electronic and optoelectronic properties have been observed in Weyl semimetals, which make them highly promising for future electronic, spintronic, and optoelectronic devices. Here, we report the generation of surface plasmon polaritons at visible wavelengths in the topological Weyl semimetal WTe2. We find that the plasmonic resonance can be distinctly formed in the WTe2 nanograting configuration. The resonance wavelength is dependent on the width of the nanograting. Our finding in the Weyl semimetal will open a new avenue for plasmonic control and devices in high frequency region.

Zinc (Zn) metal is regarded as a promising anode material for aqueous batteries owing to its high natural abundance, high theoretical capacity and low redox potential. However, aqueous Zn metal anodes suffer from poor reversibility, as shown by their low Coulombic efficiency (CE) and dendrite growth during long-term plating/stripping. In this study, we report that a thin metallic Cu or Ag interfacial layer, made by a facile thermal evaporation method, can enable highly reversible and nondendritic plating/stripping of Zn metal anodes in aqueous batteries. This is attributed to the synergy of fast Zn-ion migration through the tiny gaps in the interfacial layer as well as its high interfacial affinity for Zn metal. High average CE of 99.7% are achieved over 3000 plating/stripping cycles at 10 mA cm−2 and 1 mAh cm−2. The modified Zn anode can stably cycle for more than 2500 cycles (5000 h) of plating/stripping at 1 mA cm−2 and a 500 cycle-life is realized for a full cell paired with a MnO2 cathode. This finding opens up a promising avenue to develop the next-generation Zn metal-based energy storage technologies.

Since the discovery of iron-based superconductors, a new chapter has been opened in the history of the development of high temperature superconductivity. In the past decade, there have been remarkable achievements in the theory, experiments, and applications of iron-based superconductors, and our understanding of the mechanism of superconductivity has been deeply enriched. Here, we review the research progress on high-pressure studies on the superconductivity, flux pinning, and vortex dynamics of iron-based superconductor families. The topics include pressure-induced superconductivity, raising the superconducting transition temperature, pressure-induced elimination and re-emergence of superconductivity, the effects of phase separation on superconductivity, increasing the critical current density, significantly suppressing vortex creep, and reducing the size of the flux bundles.

Holography has extremely extensive applications in conventional optical instruments spanning optical microscopy and imaging, three-dimensional displays and metrology. To integrate holography with modern low-dimensional electronic devices, holograms need to be thinned to a nanometric scale. However, to keep a pronounced phase shift modulation, the thickness of holograms has been generally limited to the optical wavelength scale, which hinders their integration with ultrathin electronic devices. Here, we break this limit and achieve 60 nm holograms using a topological insulator material. We discover that nanometric topological insulator thin films act as an intrinsic optical resonant cavity due to the unequal refractive indices in their metallic surfaces and bulk. The resonant cavity leads to enhancement of phase shifts and thus the holographic imaging. Our work paves a way towards integrating holography with flat electronic devices for optical imaging, data storage and information security., Holograms generally need to be as thick as a wavelength of light to introduce the necessary optical phase shifts that create true three-dimensional images. Here, Yue et al. use a high-index topological insulator material to create a resonant optical cavity and thin holograms to the nanometre scale.

In recent years, atomically thin superconductors, including atomically thin elemental superconductors, single layer FeSe films, and few-layer cuprate superconductors, have been studied extensively. This hot research field is mainly driven by the discovery of significant superconductivity enhancement and high-temperature interface superconductivity in single-layer FeSe films epitaxially grown on SrTiO3 substrates in 2012. This study has attracted tremendous research interest and generated more studies focusing on further enhancing superconductivity and finding the origin of the superconductivity. A few years later, research on atomically thin superconductors has extended to cuprate superconductors, unveiling many intriguing properties that have neither been proposed or observed previously. These new discoveries challenge the current theory regarding the superconducting mechanism of unconventional superconductors and indicate new directions on how to achieve high-transition-temperature superconductors. Herein, this exciting recent progress is briefly discussed, with a focus on the recent progress in identifying new atomically thin superconductors.

We investigated the magnetotransport properties of Fe-doped topological insulator $\mathrm{S}{\mathrm{b}}_{1.96}\mathrm{F}{\mathrm{e}}_{0.04}\mathrm{T}{\mathrm{e}}_{3}$ single crystals. With doping, the band structure changes significantly and multiple Fermi pockets become evident in the Shubnikov--de Haas oscillations, in contrast to the single frequency detected for pure $\mathrm{S}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{3}$. Using complementary density functional theory calculations, we identify an additional bulk hole pocket introduced at the \ensuremath{\Gamma} point which originates from the chemical distortion associated with the Fe dopant. Experimentally, both doped and undoped samples are hole-carrier dominated; however, Fe doping also reduces the carrier density and mobility. The angle dependent quantum oscillations of $\mathrm{S}{\mathrm{b}}_{1.96}\mathrm{F}{\mathrm{e}}_{0.04}\mathrm{T}{\mathrm{e}}_{3}$ were analyzed to characterize the complex Fermi surface and isolate the dimensionality of each SdH feature. Among those components, we found two oscillations frequencies, which related to two Fermi pockets are highly angle dependent. Moreover, the fermiology changes via Fe doping and may also provide a different Berry phase, as demonstrated by the Landau fan diagram, thus indicating a rich complexity in the underlying electronic structure.

Topological insulators are quantum materials that have an insulating bulk state and a topologically protected metallic surface state with spin and momentum helical locking and a Dirac-like band structure. Unique and fascinating electronic properties, such as the quantum spin Hall effect, quantum anomalous Hall effect, and topological magnetoelectric effect, as well as magnetic monopole images and Majorana fermions, have been observed in the topological insulator materials. With these unique properties, topological insulator materials have great potential applications in spintronics and quantum information processing, as well as magnetoelectric devices with higher efficiency and lower energy consumption. On the other hand, topological insulator materials also exhibit a number of excellent optical properties, including Kerr and Faraday rotation, ultrahigh bulk refractive index, near-infrared frequency transparency, unusual electromagnetic scattering, and ultra-broadband surface plasmon resonances. Specifically, Dirac plasmon excitations have been observed in Bi2Se3 micro-ribbon arrays at THz frequencies. Ultraviolet and visible frequency plasmonics have been observed in nanoslit and nanocone arrays of Bi1.5Sb0.5Te1.8Se1.2 crystals. High transparency has been observed in Bi2Se3 nanoplates. An ultrahigh refractive index has been observed in bulk Bi1.5Sb0.5Te1.8Se1.2 crystals as well as in Sb2Te3 thin films. These excellent optical properties mean that topological insulator materials are suitable for various optoelectronic devices, including plasmonic solar cells, ultrathin holograms, plasmonic and Fresnel lens, broadband photodetectors, and nanoscale waveguides. In this chapter, we focus on the excellent electronic and optical properties of topological insulator materials and their wide applications in advanced optoelectronic devices.

Topological insulators as new emerging building blocks in electronics and photonics present promising prospects for exciting surface plasmons and enhancing light-matter interaction. Thus, exploring the visible-range plasmonic response of topological insulators is significant to reveal their optical characteristics and broaden their applications at high frequencies. Herein, we report the experimental demonstration of a visible-range surface plasmon resonance (SPR) effect on an antimony telluride (Sb2Te3) topological insulator film. The results show that the SPR can be excited with a relatively small incident angle in the Kretschmann configuration based on the Sb2Te3 film. Especially, we develop an impactful digital holographic imaging system based on the topological insulator SPR and realize the dynamic monitoring of refractive index variation. Compared with the traditional SPR, the Sb2Te3-based SPR possesses a broader measurement range. Our findings open a new avenue for exploring the optical physics and practical applications of topological insulators, such as environmental and biochemical sensing.

We study magnetotransport in a rare earth doped topological insulator, Sm0.1Sb1.9Te3 single crystals, under magnetic fields up to 14 T. It is found that that the crystals exhibit Shubnikov de Haas oscillations in their magneto-transport behaviour at low temperatures and high magnetic fields. The SdH oscillations result from the mixed contributions of bulk and surface states. We also investigate the SdH oscillations in different orientations of the magnetic field, which reveals a three dimensional Fermi surface topology. By fitting the oscillatory resistance with the Lifshitz Kosevich theory, we draw a Landau-level fan diagram that displays the expected nontrivial phase. In addition, the density functional theory calculations shows that Sm doping changes the crystal structure and electronic structure compared with pure Sb2Te3. This work demonstrates that rare earth doping is an effective way to manipulate the Fermi surface of topological insulators. Our results hold potential for the realization of exotic topological effects in magnetic topological insulators., Comment: 16 pages, 5 figures

We report a comprehensive study of magneto-transport properties in MoSi$_2$ bulk and thin films. Textured MoSi$_2$ thin films of around 70 nm were deposited on silicon substrates with different orientations. Giant magnetoresistance of 1000% was observed in sintered bulk samples while MoSi$_2$ single crystals exhibit a magnetoresistance (MR) value of 800% at low temperatures. At the low temperatures, the MR of the textured thin films show weak anti-localization behaviour owing to the spin orbit coupling effects. Our first principle calculation show the presence of surface states in this material. The resistivity of all the MoSi$_2$ thin films is significantly low and nearly independent of the temperature, which is important for electronic devices.

We study magneto-transport phenomena in two rare-earth doped topological insulators, SmxFexSb2-2xTe3 and SmxBi2-xTe2Se single crystals. The magneto-transport behaviours in both compounds exhibit a novel crossover between weak anti-localization (positive magnetoresistance) and weak localization (negative magnetoresistance) with changes in temperatures and magnetic fields. The weak localization is caused by rare-earth-doping induced magnetization, and the weak anti-localization originates from topologically protected surface states. The transition from weak localization to weak anti-localization demonstrates a gap opening at the Dirac point of the surface states in the quantum diffusive regime. This work demonstrates an effective way to manipulate the magneto-transport properties of the topological insulators by rare-earth element doping. Magnetometry measurements indicate that the Sm-dopant alone is paramagnetic, whereas the co-doped Fe-Sm state has short-range antiferromagnetic order. Our results demonstrate the potential to realize exotic topological effects and magneto-electric effects in gapped surface states of rare earth doped topological insulators.

As newly emerging nanomaterials, topological insulators with unique conducting surface states that are protected by time-reversal symmetry present excellent prospects in electronics and photonics. The active control of light absorption in topological insulators are essential for the achievement of novel optoelectronic devices. Herein, we investigate the controllable light absorption of topological insulators in Tamm plasmon multilayer systems composed of a Bi1.5Sb0.5Te1.8Se1.2 (BSTS) film and a dielectric Bragg mirror with a graphene-involved defect layer. The results show that an ultranarrow electromagnetically induced transparency (EIT)-like window can be generated in the broad absorption spectrum. Based on the EIT-like effect, the Tamm plasmon enhanced light absorption of topological insulators can be dynamically tuned by adjusting the gate voltage on graphene in the defect layer. These results will pave a new avenue for the realization of topological insulator-based active optoelectronic functionalities, for instance light modulation and switching.

The surfaces of Sb2Te3 topological insulator crystals were implanted using a 40 keV chromium ion beam. To facilitate uniform doping, the Sb2Te3 was passivated with a thin TiO2 film before the implantation step. The resulting chemical structure was studied using atomic-resolution transmission electron microscopy. A fluence of 7 × 1015 ions/cm2 at 40 keV lead to amorphization of the Sb2Te3 surface, with chromium predominantly incorporated in the amorphous layer. Heating to 200 °C caused the amorphous region to recrystallize and led to the formation of a thin chromium-rich interfacial layer. Near-edge x-ray absorption spectroscopy indicates a uniform valence state of Cr3+ throughout, with no evidence of metallic clustering. High-temperature superparamagnetic behavior was detected up to 300 K, with an increased magnetic moment below 50 K.

Complementary metal–oxide–semiconductor (CMOS) technology has provided a highly sensitive detection platform for high-resolution optical imaging, sensing and metrology. Although the detection of optical beams carrying angular momentum have been explored with nanophotonic methods, the metrology of optical angular momentum has been limited to bulk optics. We demonstrate angular-momentum nanometrology through the spatial displacement engineering of plasmonic angular momentum modes in a CMOS-compatible plasmonic topological insulator material. The generation and propagation of surface plasmon polaritons on the surface of an ultrathin topological insulator Sb2Te3 film with a thickness of 100 nm is confirmed, exhibiting plasmonic figures of merit superior to noble metal plasmonics in the ultraviolet-visible frequency range. Angular-momentum nanometrology with a low crosstalk of less than −20 dB is achieved. This compact high-precision angular-momentum nanometrology opens an unprecedented opportunity for on-chip manipulation of optical angular momentum for high-capacity information processing, ultrasensitive molecular sensing, and ultracompact multi-functional optoelectronic devices., Multiplexed vortex light beams are promising for optical communications, but efficient mode sorting is so far limited to bulk optics. Here the authors develop a scalable vortex beam sorter that uses a plasmonic topological insulator structure to spatially separate the modes to resolve them on a standard CMOS detector.

We propose the use of three-dimensional direct laser writing to create neuron-inspired structures. The experimental realization of neuron-inspired structures 10 times smaller than biological neurons is achieved using two-photon direct laser writing.

High refractive-index double-gyroid photonic crystals with broken inversion symmetry exhibit two pairs of Type I Weyl points. We realize micron-scale photonic crystals exhibiting Weyl points by means of laser direct writing and high refractive-index coating.

Topological insulators as relatively new quantum materials with the topologically protected conducting Dirac surface state reveal fantastic electronic and photonic characteristics. The photonic behaviors of topological insulators are particularly significant for exploring their optical phenomena and functional devices. Here, we present the generation of Tamm plasmon polaritons (TPPs) in a topological insulator multilayer structure consisting of a Bi1.5Sb0.5Te1.8Se1.2 (BSTS) nanofilm and a one-dimensional photonic crystal (PC). The results illustrate that the TPP electric field can locally concentrate between the BSTS nanofilm and PC, contributing to the improved light-BSTS interaction with a 3-fold enhancement of light absorption. It is also found that the near-infrared TPP response can be dynamically tailored by adjusting the PC layer thickness, BSTS nanofilm thickness, and angle of incident light. The theoretical calculations are in excellent agreement with the numerical simulations. Additionally, the TPP field intensity and light-topological insulator interaction are capable of being further reinforced by introducing a dielectric spacer between the BSTS nanofilm and PC. Our results will enrich the optical characteristics and application potential of topological insulators.Topological insulators as relatively new quantum materials with the topologically protected conducting Dirac surface state reveal fantastic electronic and photonic characteristics. The photonic behaviors of topological insulators are particularly significant for exploring their optical phenomena and functional devices. Here, we present the generation of Tamm plasmon polaritons (TPPs) in a topological insulator multilayer structure consisting of a Bi1.5Sb0.5Te1.8Se1.2 (BSTS) nanofilm and a one-dimensional photonic crystal (PC). The results illustrate that the TPP electric field can locally concentrate between the BSTS nanofilm and PC, contributing to the improved light-BSTS interaction with a 3-fold enhancement of light absorption. It is also found that the near-infrared TPP response can be dynamically tailored by adjusting the PC layer thickness, BSTS nanofilm thickness, and angle of incident light. The theoretical calculations are in excellent agreement with the numerical simulations. Additionally, the T...

A new type of plasmonic nanostructures with topologically protected metallic shells and high–refractive index dielectric cores., Topological insulators are a new class of quantum materials with metallic (edge) surface states and insulating bulk states. They demonstrate a variety of novel electronic and optical properties, which make them highly promising electronic, spintronic, and optoelectronic materials. We report on a novel conic plasmonic nanostructure that is made of bulk-insulating topological insulators and has an intrinsic core-shell formation. The insulating (dielectric) core of the nanocone displays an ultrahigh refractive index of up to 5.5 in the near-infrared frequency range. On the metallic shell, plasmonic response and strong backward light scattering were observed in the visible frequency range. Through integrating the nanocone arrays into a-Si thin film solar cells, up to 15% enhancement of light absorption was predicted in the ultraviolet and visible ranges. With these unique features, the intrinsically core-shell plasmonic nanostructure paves a new way for designing low-loss and high-performance visible to infrared optical devices.

We report computer-generated holography in ultrathin topological insulator films. With different refractive index in metallic surface and dielectric bulk, the ultrathin topological insulator film serves as a natural optical resonant cavity, which remarkably enhances the phase modulations and the diffraction efficiency in the holograms.

Anisotropic interlayer magneto-transport properties have been studied over a broad range of temperatures and magnetic fields in p-type Sb2Te3 single crystals. Giant interlayer magnetoresistance (MR) of up to 400% was observed, which exhibits quadratic field dependences in low fields and becomes linear at high fields without any trend towards saturation. The interlayer MR displays strong anisotropy and is attributable to the anisotropy of the Fermi surface. The observed giant anisotropic interlayer MR could find applications in p-type Sb2Te3 based magneto-electronic devices.

Biological systems have been using nanometre-scale architectures to produce striking optical effects and the way these natural photonic structures manipulate the flow of light has inspired many technological applications. Nevertheless, the applications of these natural structures in photonic devices require appropriate fabrication techniques able to tailor and enhance the natural features of the biological systems. In this communication the authors report on the development of a layered-composite nanometric Sb2Te3 material for the realization of bio-inspired three-dimensional chiral photonic crystals exceeding their natural optical properties. The authors demonstrate that the deposition of Sb2Te3 on laser written polymer templates can fabricate biomimetic photonic structures with superior control over size, periodicity, filling fraction, and refractive index, compared with the natural counterparts. In this way the refractive index of the photonic crystals can be increased by 100% and the photonic bandgap for use in practical devices can be precisely engineered. These bio-inspired structures can be useful in the investigation of new branches of photonics and in the development of novel chiral optical devices capable of manipulating photons in three dimensions.