Conformal structure-preserving method for damped nonlinear Schrödinger equation
Fractal dynamics in the ionization of helium Rydberg atoms
We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory. By introducing a fractal approach to describe the chaotic dynamical behavior of the ionization, we identify the fractal self-similarity structure of the escape time versus the distribution of the initial launch angles of electrons, and find that the self-similarity region shifts toward larger initial launch angles with a decrease in the scaled energy. We connect the fractal structure of the escape time plot to the escape dynamics of ionized electrons. Of particular note is that the fractal dimensions are sensitively controlled by the scaled energy and magnetic field, and exhibit excellent agreement with the chaotic extent of the ionization systems for both helium and hydrogen Rydberg atoms. It is shown that, besides the electric and magnetic fields, core scattering is a primary factor in the fractal dynamics.
General coarsened measurement references for revelation of a classical world
Amplifying and freezing of quantum coherence using weak measurement and quantum measurement reversal
Stopping time of a one-dimensional bounded quantum walk
The stopping time of a one-dimensional bounded classical random walk (RW) is defined as the number of steps taken by a random walker to arrive at a fixed boundary for the first time. A quantum walk (QW) is a non-trivial generalization of RW, and has attracted a great deal of interest from researchers working in quantum physics and quantum information. In this paper, we develop a method to calculate the stopping time for a one-dimensional QW. Using our method, we further compare the properties of stopping time for QW and RW. We find that the mean value of the stopping time is the same for both of these problems. However, for short times, the probability for a walker performing a QW to arrive at the boundary is larger than that for a RW. This means that, although the mean stopping time of a quantum and classical walker are the same, the quantum walker has a greater probability of arriving at the boundary earlier than the classical walker.
Cryptanalysis of quantum broadcast communication and authentication protocol with a one-time pad
Chang et al. [Chin. Phys. B 23 010305 (2014)] have proposed a quantum broadcast communication and authentication protocol. However, we find that an intercept-resend attack can be preformed successfully by a potential eavesdropper, who will be able to destroy the authentication function. Afterwards, he or she can acquire the secret transmitted message or even modify it while escaping detection, by implementing an efficient man-in-the-middle attack. Furthermore, we show a simple scheme to defend this attack, that is, applying non-reusable identity strings.
Evolution of the vortex state in the BCS-BEC crossover of a quasi two-dimensional superfluid Fermi gas
Cluster synchronization of community network with distributed time delays via impulsive control
Application of the nonlinear time series prediction method of genetic algorithm for forecasting surface wind of point station in the South China Sea with scatterometer observations
Prompt efficiency of energy harvesting by magnetic coupling of an improved bi-stable system
Anomalous transport in fluid field with random waiting time depending on the preceding jump length
Theoretics-directed effect of copper or aluminum content on the ductility characteristics of Al-based (Al3Ti,AlTi,AlCu,AlTiCu2) intermetallic compounds
Isotope shift calculations for D lines of stable and short-lived lithium nuclei
The isotope shifts (ISs) for the 2s2S1/2 to 2p2PJ (J=1/2, 3/2) transitions of the lithium nuclei including the stable and short-lived isotopes are calculated based on the multi-configuration Dirac-Hartree-Fock method and the relativistic configuration interaction approach. The results are in good agreement with the previous theoretical and experimental results within a deviation less than 0.05%. The methods used here could be applied to the IS calculations for other heavier Li-like ions and few-electron systems.
High-order harmonic generation of CO2 with different vibrational modes in an intense laser field
We apply the strong-field Lewenstein model to demonstrate the high-order harmonic generation of CO2 with three vibrational modes (balance vibration, bending vibration, and stretching vibration) driven by an intense laser field. The results show that the intensity of harmonic spectra is sensitive to molecular vibrational modes, and the high harmonic efficiency with stretching vibrational mode is the strongest. The underlying physical mechanism of the harmonic emission can be well explained by the corresponding ionization yield and the time-frequency analysis. Finally, we demonstrate the attosecond pulse generation with different vibrational modes and an isolated attosecond pulse with a duration of about 112 as is generated.
Fano resonance and magneto-optical Kerr rotaion in periodic Co/Ni complex plasmonic nanostructure
We report a pure ferromagnetic metallic magnetoplasmonic structure consisting of two-dimensional ordered Ni nanodisks array on Co film. With a sufficient height of the nanodisks, a steep and asymmetric Fano resonance can be excited in this structure. We attribute the fascinating spectral lineshape to the strong coupling between the excitation of surface plasmon polaritons at the interface and the localized surface plasmon resonance of nanodisks. The conclusion is fully confirmed by spectrum measurements in nanostructures with different heights. Furthermore, the enhancement and sign of the magneto-optical Kerr rotation in this structure are significantly modified by the Fano resonance.
Landau-Zener model for electron loss of low-energy negative fluorine ions to surface cations during grazing scattering on a LiF (001) surface
Semi-analytical model for quasi-double-layer surface electrode ion traps
Theoretical derivation and simulation of a versatileelectrostatic trap for cold polar molecules
An optimized ion trap geometry to measure quadrupole shifts of 171Yb+ clocks
We propose a new ion-trap geometry to carry out accurate measurements of the quadrupole shifts in the 171Yb ion. This trap will minimize the quadrupole shift due to the harmonic component of the confining potential by an order of magnitude. This will be useful to reduce the uncertainties in the clock frequency measurements of the 6s 2S1/2→4f136s2 2F7/2 and 6s 2S1/2→5d 2D3/2 transitions, from which we can deduce the precise values of the quadrupole moments (Θs) of the 4f136s2 2F7/2 and 5d 2D3/2 states. Moreover, it may be able to affirm the validity of the measured Θ value of the 4f136s2 2F7/2 state, for which three independent theoretical studies defer almost by one order of magnitude from the measurement. We also calculate Θs using the relativistic coupled-cluster (RCC) method. We use these Θ values to estimate the quadrupole shift that can be measured in our proposed ion trap experiment.
Application of optical diffraction method in designing phase plates
Self-calibration wavelength modulation spectroscopy for acetylene detection based on tunable diode laser absorption spectroscopy
Theoretical simulation of 87Rb absorption spectrum in a thermal cell
Observation of multi-Raman gain resonances in rubidium vapor
Two-dimensional gain cross-grating based on spatial modulation of active Raman gain
Effects of magnetic field on photon-induced quantum transport in a single dot-cavity system
An efficient continuous-wave YVO4/Nd: YVO4/YVO4 self-Raman laser pumped by a wavelength-locked 878.9 nm laser diode
Research of the use of silver nanowires as a current spreading layer on vertical-cavity surface-emitting lasers
Coupled-resonator-induced transparency in two microspheres as the element of angular velocity sensing
Tracking molecular structure deformation of nitrobenzene and its torsion vibration coupling by intense pumping CARS
The structural deformation induced by intense laser field of liquid nitrobenzene (NB) molecule, a typical molecule with restricting internal rotation, is tracked by time- and frequency-resolved coherent anti-Stokes. Raman spectroscopy (CARS) technique with an intense pump laser. The CARS spectra of liquid NB show that the NO2 torsional mode couples with the NO2 symmetric stretching mode, and the NB molecule undergoes ultrafast structural deformation with a relaxation time of 265 fs. The frequency of NO2 torsional mode in liquid NB (42 cm-1) at room temperature is found from the sum and difference combination bands involving the NO2 symmetric stretching mode and torsional mode in time- and frequency-resolved CARS spectra.
Ultra broadband flat dispersion tailoring on reversed-rib chalcogenide glass waveguide
Optimizing calculation of phase screen distribution with minimum condition along an inhomogeneous turbulent path
High-reflectivity high-contrast grating focusing reflector on silicon-on-insulator wafer
A proposal for the generation of optical frequency comb in temperature insensitive microcavity
Turbulence mitigation scheme based on multiple-user detection in an orbital-angular-momentum multiplexed system
Plasmon-phonon coupling in graphene-hyperbolic bilayer heterostructures
Low band gap frequencies and multiplexing properties in 1D and 2D mass spring structures
Temperature-dependent specific heat of suspended platinum nanofilms at 80-380 K
Metallic nanofilms are important components of nanoscale electronic circuits and nanoscale sensors. The accurate characterization of the thermophysical properties of nanofilms is very important for nanoscience and nanotechnology. Currently, there is very little specific heat data for metallic nanofilms, and the existing measurements indicate distinct differences according to the nanofilm size. The present work reports the specific heats of 40-nm-thick suspended platinum nanofilms at 80-380 K and ~5×10-4 Pa using the 3ω method. Over 80-380 K, the specific heats of the Pt nanofilms range from 166-304 J/(kg·K), which are 1.65-2.60 times the bulk values, indicating significant size effects. These results are useful for both scientific research in nanoscale thermophysics and evaluating the transient thermal response of nanoscale devices.
Generalized Birkhoffian representation of nonholonomic systems and its discrete variational algorithm
Molecular dynamics simulation of structural change at metal/semiconductor interface induced by nanoindenter
Induced magnetic field stagnation point flow of nanofluid past convectively heated stretching sheet with Buoyancy effects
Three-dimensional detonation cellular structures in rectangular ducts using an improved CESE scheme
A divertor plasma configuration design method for tokamaks
One-dimensional hybrid simulation of the electrical asymmetry effectcaused by the fourth-order harmonic in dual-frequencycapacitively coupled plasma
Transport coefficients and mechanical response in hard-disk colloidal suspensions
We investigate the transport properties and mechanical response of glassy hard disks using nonlinear Langevin equation theory. We derive expressions for the elastic shear modulus and viscosity in two dimensions on the basis of thermal-activated barrier-hopping dynamics and mechanically accelerated motion. Dense hard disks exhibit phenomena such as softening elasticity, shear-thinning of viscosity, and yielding upon deformation, which are qualitatively similar to dense hard-sphere colloidal suspensions in three dimensions. These phenomena can be ascribed to stress-induced “landscape tilting”. Quantitative comparisons of these phenomena between hard disks and hard spheres are presented. Interestingly, we find that the density dependence of yield stress in hard disks is much more significant than in hard spheres. Our work provides a foundation for further generalizing the nonlinear Langevin equation theory to address slow dynamics and rheological behavior in binary or polydisperse mixtures of hard or soft disks.
Direct observation of the carrier transport process in InGaN quantum wells with a pn-junction
A new mechanism of light-to-electricity conversion that uses InGaN/GaN QWs with a p-n junction is reported. According to the well established light-to-electricity conversion theory, quantum wells (QWs) cannot be used in solar cells and photodetectors because the photogenerated carriers in QWs usually relax to ground energy levels, owing to quantum confinement, and cannot form a photocurrent. We observe directly that more than 95% of the photoexcited carriers escape from InGaN/GaN QWs to generate a photocurrent, indicating that the thermionic emission and tunneling processes proposed previously cannot explain carriers escaping from QWs. We show that photoexcited carriers can escape directly from the QWs when the device is under working conditions. Our finding challenges the current theory and demonstrates a new prospect for developing highly efficient solar cells and photodetectors.
Quantitative determination of anti-structured defects applied to alloys of a wide chemical range
Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO2 single crystals
Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO2 single crystals (SCs). To tune their magnetism, Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively. The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO2. Meanwhile, a new CuO-like species present in the sample was found to be dissolved after the post-irradiation. Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions, while these ions are directly involved in boosting the absorption in the visible region.
Thermophysical properties of iridium at finite temperature
The bulk properties of materials in an extreme environment such as high temperature and high pressure can be understood by studying anharmonic effects due to the vibration of lattice ions and thermally excited electrons. In this spirit, in the present paper, anharmonic effects are studied by using the recently proposed mean-field potential (MFP) approach and Mermin functional which arise due to the vibration of lattice ions and thermally excited electrons, respectively. The MFP experienced by a wanderer atom in the presence of surrounding atoms is constructed in terms of cold energy using the local form of the pseudopotential. We have calculated the temperature variation of several thermophysical properties in an extreme environment up to melting temperature. The results of our calculations are in excellent agreement with the experimental findings as well as the theoretical results obtained by using first principle methods. We conclude that presently used conjunction scheme (MFP+pseudopotential) is simple computationally, transparent physically, and accurate in the sense that the results generated are comparable and sometimes better than the results obtained by first principle methods. Local pseudopotential used is transferable to extreme environment without adjusting its parameters.
First-principles study of He trapping in η-Fe2C
Kernel polynomial representation for imaginary-time Green's functions in continuous-time quantum Monte Carlo impurity solver
Inspired by the recently proposed Legendre orthogonal polynomial representation for imaginary-time Green's functions G(τ), we develop an alternate and superior representation for G(τ) and implement it in the hybridization expansion continuous-time quantum Monte Carlo impurity solver. This representation is based on the kernel polynomial method, which introduces some integral kernel functions to filter the numerical fluctuations caused by the explicit truncations of polynomial expansion series and can improve the computational precision significantly. As an illustration of the new representation, we re-examine the imaginary-time Green's functions of the single-band Hubbard model in the framework of dynamical mean-field theory. The calculated results suggest that with carefully chosen integral kernel functions, whether the system is metallic or insulating, the Gibbs oscillations found in the previous Legendre orthogonal polynomial representation have been vastly suppressed and remarkable corrections to the measured Green's functions have been obtained.
Current spreading in GaN-based light-emitting diodes
Strain-induced magnetism in ReS2 monolayer with defects
We investigate the effects of strain on the electronic and magnetic properties of ReS2 monolayer with sulfur vacancies using density functional theory. Unstrained ReS2 monolayer with monosulfur vacancy (VS) and disulfur vacancy (V2S) both are nonmagnetic. However, as strain increases to 8%, VS-doped ReS2 monolayer appears a magnetic half-metal behavior with zero total magnetic moment. In particular, for V2S-doped ReS2 monolayer, the system becomes a magnetic semiconductor under 6% strain, in which Re atoms at vicinity of vacancy couple anti-ferromagnetically with each other, and continues to show a ferromagnetic metal characteristic with total magnetic moment of 1.60μ B under 7% strain. Our results imply that the strain-manipulated ReS2 monolayer with VS and V2S can be a possible candidate for new spintronic applications.
Crossover of large to small radius polaron in ionic crystals
The crossover of large to small radius polaron is studied in terms of the inverse-relaxation time and temperature. It is found that the small radius polaron exists at higher temperature than the large radius polaron. A formula which relates the inverse-relaxation time to the ratio of arbitrary temperature and Debye temperature of the crystal is derived. The polaron crossover temperatures in NaCl and KBr are found from plotted graphs. The straight line emerging at the Debye temperature TD of a graph reflects the increase of the inverse relaxation time for increasing temperature up to the collapse of the small radius polaron. The relationship between the small and large radius polarons is found and known ratios of the effective and the bare masses of the electrons for the two substances are used to validate our results. The small radius polaron's mass is later compared with the mass obtained from the hopping formula and is found to be approximately equal. Finally, we point out that the crossover temperature is material-specific since it depends on the Debye and the effective dielectric function.
Spin noise spectroscopy of rubidium atomic gas under resonant and non-resonant conditions
Small-signal modeling of GaN HEMT switch with a new intrinsic elements extraction method
Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire
Electronic transport of bilayer graphene with asymmetry line defects
In this paper, we study the quantum properties of a bilayer graphene with (asymmetry) line defects. The localized states are found around the line defects. Thus, the line defects on one certain layer of the bilayer graphene can lead to an electric transport channel. By adding a bias potential along the direction of the line defects, we calculate the electric conductivity of bilayer graphene with line defects using the Landauer-Büttiker theory, and show that the channel affects the electric conductivity remarkably by comparing the results with those in a perfect bilayer graphene. This one-dimensional line electric channel has the potential to be applied in nanotechnology engineering.
Effects of fluorine-based plasma treatment and thermal annealing on high-Al content AlGaN Schottky contact
Recessed-gate quasi-enhancement-mode AlGaN/GaN high electron mobility transistors with oxygen plasma treatment
Charge transport and bipolar switching mechanismin a Cu/HfO2/Pt resistive switching cell
Spin-dependent thermoelectric effect and spin battery mechanism in triple quantum dots with Rashba spin-orbital interaction
First-principles calculation of the structural,electronic,and magnetic properties of cubic perovskite RbXF3(X=Mn,V,Co,Fe)
Spatially resolved gap closing in single Josephson junctions constructed on Bi2Te3 surface Hot!
Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators. Previously, we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi2Te3 surface. In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi2Te3 surface.
Interplay between spin frustration and magnetism in the exactly solved two-leg mixed spin ladder
We study a mixed spin-( 3/2, 1) ladder system with antiferromagnetic rung coupling and next-nearest-neighbor interaction. The exactly solved Ising-chain model is employed to investigate the ground-state properties and thermodynamics of the low-dimensional ladder system. Our results show that the competition between different exchange couplings brings in a large variety of ground states characterized by various values of normalized magnetization equal to 0, 1/5, 2/5, 3/5, 1. Moreover, an interesting double-peak structure is also detected in the thermal dependence of magnetic susceptibility and specific heat when the frustration comes into play. It is shown that the double-peak phenomenon at zero-field for the case of AF2 ground-state arises from the very strong antiferromagnetic rung coupling, while other cases are attributed to the excitations induced by temperature and external field around the phase boundary.
Size-dependent exchange bias in single phase Mn3O4 nanoparticles
Glassy magnetic behavior and exchange bias phenomena are observed in single phase Mn3O4 nanoparticles. Dynamics scaling analysis of the ac susceptibility and the Henkel plot indicate that the observed glassy behavior at low temperature can be understood by taking into account the intrinsic behavior of the individual particles consisting of a ferrimagnetic (FIM) core and a spin-glass surface layer. Field-cooled magnetization hysteresis loops display both horizontal and vertical shifts. Dependence of the exchange bias field (HE) on the cooling field shows an almost undamped feature up to 70 kOe, indicating the stable exchange bias state in Mn3O4.HE increases as the particle size decreases due to the higher surface/volume ratio. The occurrence of the exchange bias can be attributed to the pinning effect of the frozen spin-glass surface layer upon the FIM core.
Dy substitution effect on the temperature dependences of magnetostriction in Pr1-xDyxFe1.9 alloys
The temperature dependences of magnetostriction in Pr1-xDyxFe1.9 (0≤x≤1.0) alloys between 5 K and 300 K were investigated. An unusual decrease of magnetostriction with temperature decreasing was found in Pr-rich alloys (0≤x≤0.2), due to the change of the easy magnetization direction (EMD). Dy substitution reduces the magnetostriction in high-magnetic field (10 kOe≤H≤90 kOe) at 5 K, while a small amount of Dy substitution (x=0.05) is beneficial to increasing the magnetostriction in low-magnetic field between 10 K and 50 K. This makes the alloys a potential candidate for low temperature applications.
Improvement in coercivity,thermal stability,and corrosion resistance of sintered Nd-Fe-B magnets with Dy80Ga20 intergranular addition
Lumped modeling with circuit elements for nonreciprocal magnetoelectric tunable band-pass filter
Effects of thickness and annealing condition on magnetic properties and thermal stabilities of Ta/Nd/NdFeB/Nd/Ta sandwiched films
Threshold resistance switching in silicon-rich SiOx thin films
Exchange effect and magneto-plasmon mode dispersion in an anisotropic two-dimensional electronic system
Full-profile fitting of emission spectrum to determine transition intensity parameters of Yb3+: GdTaO4
The Judd-Ofelt theoretic transition intensity parameters Atpk of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence. It is very difficult to determine them with emission or absorption spectra for a long time. A “full profile fitting” method to obtain Atpk in solids with its emission spectrum is proposed, in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability, line profile function, instrument measurement constant and transition center frequency or wavelength, and the whole experimental emission spectrum is the sum of all transitions. In this way, the emission spectrum is expressed as a function with the independent variables intensity parameters Atpk, full width at half maximum (FWHM) of profile functions, instrument measurement constant, wavelength, and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered. The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting Atpk and other parameters. Employing this method obviates measurement of the absolute emission spectrum intensity. It also eliminates dependence upon the number of emission transition peaks. Every experiment point in emission spectra, which usually have at least hundreds of data points, is the function with variables Atpk and other parameters, so it is usually viable to determine Atpk and other parameters using a large number of experimental values. We applied this method to determine twenty-five Atpk of Yb3+ in GdTaO4. The calculated and experiment energy lifetimes, experimental and calculated emission spectrum are very consistent, indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions' emission spectrum. The calculated emission cross sections of Yb3+:GdTaO4 also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.
Engineering optical gradient force from coupled surface plasmon polariton modes in nanoscale plasmonic waveguides
Effect of Mo capping layers thickness on the perpendicular magnetic anisotropy in MgO/CoFeB based top magnetic tunnel junction structure
Restructuring of plasmonic nanoparticle aggregates with arbitrary particle size distribution in pulsed laser fields
Quantum transport properties of the three-dimensional Dirac semimetal Cd3As2 single crystals
The discovery of the three-dimensional Dirac semimetals have expanded the family of topological materials, and attracted massive attentions in recent few years. In this short review, we briefly overview the quantum transport properties of a well-studied three-dimensional Dirac semimetal, Cd3As2. These unusual transport phenomena include the unexpected ultra-high charge mobility, large linear magnetoresistivity, remarkable Shubnikov-de Hass oscillations, and the evolution of the nontrivial Berry's phase. These quantum transport properties not only reflect the novel electronic structure of Dirac semimetals, but also give the possibilities for their future device applications.
Topological nodal line semimetals
We review the recent, mainly theoretical, progress in the study of topological nodal line semimetals in three dimensions. In these semimetals, the conduction and the valence bands cross each other along a one-dimensional curve in the three-dimensional Brillouin zone, and any perturbation that preserves a certain symmetry group (generated by either spatial symmetries or time-reversal symmetry) cannot remove this crossing line and open a full direct gap between the two bands. The nodal line(s) is hence topologically protected by the symmetry group, and can be associated with a topological invariant. In this review, (i) we enumerate the symmetry groups that may protect a topological nodal line; (ii) we write down the explicit form of the topological invariant for each of these symmetry groups in terms of the wave functions on the Fermi surface, establishing a topological classification; (iii) for certain classes, we review the proposals for the realization of these semimetals in real materials; (iv) we discuss different scenarios that when the protecting symmetry is broken, how a topological nodal line semimetal becomes Weyl semimetals, Dirac semimetals, and other topological phases; and (v) we discuss the possible physical effects accessible to experimental probes in these materials.
Electron localization in ultrathin films of three-dimensional topological insulators
The recent discovery of three-dimensional (3D) topological insulators (TIs) has provided a fertile ground for obtaining further insights into electron localization in condensed matter systems. In the past few years, a tremendous amount of research effort has been devoted to investigate electron transport properties of 3D TIs and their low dimensional structures in a wide range of disorder strength, covering transport regimes from weak antilocalization to strong localization. The knowledge gained from these studies not only offers sensitive means to probe the surface states of 3D TIs but also forms a basis for exploring novel topological phases. In this article, we briefly review the main experimental progress in the study of the localization in 3D TIs, with a focus on the latest results on ultrathin TI films. Some new transport data will also be presented in order to complement those reported previously in the literature.
Weak antilocalization and interaction-induced localization of Dirac and Weyl Fermions in topological insulators and semimetals
Weak localization and antilocalization are quantum transport phenomena that arise from the quantum interference in disordered metals. At low temperatures, they can give distinct temperature and magnetic field dependences in conductivity, allowing the symmetry of the system to be explored. In the past few years, they have also been observed in newly emergent topological materials, including topological insulators and topological semimetals. In contrast from the conventional electrons, in these new materials the quasiparticles are described as Dirac or Weyl fermions. In this article, we review our recent efforts on the theories of weak antilocalization and interaction-induced localization for Dirac and Weyl fermions in topological insulators and topological semimetals.
Recent observations of negative longitudinal magnetoresistance in semimetal
The discovery of Dirac semimetal and Weyl semimetal has motivated a growing passion for investigating the unique magneto-transport properties in the topological materials. A Weyl semimetal can host Weyl fermions as its low-energy quasi-particle excitations, and therefore perform exotic features analogous to those in high-energy physics, such as the violation of the chiral charge conservation known as the chiral anomaly. One of the electrical transport signatures of the chiral anomaly is the Adler-Bell-Jackiw (ABJ) anomaly which presents as a negative magnetoresistance when the magnetic field and the current are parallel. Very recently, numerous experiments reported negative longitudinal magnetoresistance (NLMR) in topological materials, but the details of the measurement results are various. Here the materials and the corresponding experiment results are briefly reviewed. Besides the plausible explanation of the ABJ anomaly, some other origins of the NLMR are also discussed.
Quantum anomalous Hall effect in real materials
Under a strong magnetic field, the quantum Hall (QH) effect can be observed in two-dimensional electronic gas systems. If the quantized Hall conductivity is acquired in a system without the need of an external magnetic field, then it will give rise to a new quantum state, the quantum anomalous Hall (QAH) state. The QAH state is a novel quantum state that is insulating in the bulk but exhibits unique conducting edge states topologically protected from backscattering and holds great potential for applications in low-power-consumption electronics. The realization of the QAH effect in real materials is of great significance. In this paper, we systematically review the theoretical proposals that have been brought forward to realize the QAH effect in various real material systems or structures, including magnetically doped topological insulators, graphene-based systems, silicene-based systems, two-dimensional organometallic frameworks, quantum wells, and functionalized Sb(111) monolayers, etc. Our paper can help our readers to quickly grasp the recent developments in this field.
Thermoelectric effects and topological insulators
The recent discovery of topological insulators (TIs) offers new opportunities for the development of thermoelectrics, because many TIs (like Bi2Te3) are excellent thermoelectric (TE) materials. In this review, we will first describe the general TE properties of TIs and show that the coexistence of the bulk and boundary states in TIs introduces unusual TE properties, including strong size effects and an anomalous Seebeck effect. Importantly, the TE figure of merit zT of TIs is no longer an intrinsic property, but depends strongly on the geometric size. The geometric parameters of two-dimensional TIs can be tuned to enhance zT to be significantly greater than 1. Then a few proof-of-principle experiments on three-dimensional TIs will be discussed, which observed unconventional TE phenomena that are closely related to the topological nature of the materials. However, current experiments indicate that the metallic surface states, if their advantage of high mobility is not fully utilized, would be detrimental to TE performance. Finally, we provide an outlook for future work on topological materials, which offers great possibilities to discover exotic TE effects and may lead to significant breakthroughs in improving zT.
Topological hierarchy matters–topological matters with superlattices of defects
Topological insulators/superconductors are new states of quantum matter with metallic edge/surface states. In this paper, we review the defects effect in these topological states and study new types of topological matters–topological hierarchy matters. We find that both topological defects (quantized vortices) and non topological defects (vacancies) can induce topological mid-gap states in the topological hierarchy matters after considering the superlattice of defects. These topological mid-gap states have nontrivial topological properties, including the nonzero Chern number and the gapless edge states. Effective tight-binding models are obtained to describe the topological mid-gap states in the topological hierarchy matters.
Disorder effects in topological states: Brief review of the recent developments
Disorder inevitably exists in realistic samples, manifesting itself in various exotic properties for the topological states. In this paper, we summarize and briefly review the work completed over the last few years, including our own, regarding recent developments in several topics about disorder effects in topological states. For weak disorder, the robustness of topological states is demonstrated, especially for both quantum spin Hall states with Z2=1 and size induced nontrivial topological insulators with Z2=0. For moderate disorder, by increasing the randomness of both the impurity distribution and the impurity induced potential, the topological insulator states can be created from normal metallic or insulating states. These phenomena and their mechanisms are summarized. For strong disorder, the disorder causes a metal-insulator transition. Due to their topological nature, the phase diagrams are much richer in topological state systems. Finally, the trends in these areas of disorder research are discussed.
Two-dimensional topological insulators with large bulk energy gap
Two-dimensional (2D) topological insulators (TIs, or quantum spin Hall insulators) are special insulators that possess bulk 2D electronic energy gap and time-reversal symmetry protected one-dimensional (1D) edge state. Carriers in the edge state have the property of spin-momentum locking, enabling dissipation-free conduction along the 1D edge. The existence of 2D TIs was confirmed by experiments in semiconductor quantum wells. However, the 2D bulk gaps in those quantum wells are extremely small, greatly limiting potential application in future electronics and spintronics. Despite this limitation, 2D TIs with a large bulk gap attracted plenty of interest. In this paper, recent progress in searching for TIs with a large bulk gap is reviewed briefly. We start by introducing some theoretical predictions of these new materials and then discuss some recent important achievements in crystal growth and characterization.
Electronic properties of SnTe-class topological crystalline insulator materials
The rise of topological insulators in recent years has broken new ground both in the conceptual cognition of condensed matter physics and the promising revolution of the electronic devices. It also stimulates the explorations of more topological states of matter. Topological crystalline insulator is a new topological phase, which combines the electronic topology and crystal symmetry together. In this article, we review the recent progress in the studies of SnTe-class topological crystalline insulator materials. Starting from the topological identifications in the aspects of the bulk topology, surface states calculations, and experimental observations, we present the electronic properties of topological crystalline insulators under various perturbations, including native defect, chemical doping, strain, and thickness-dependent confinement effects, and then discuss their unique quantum transport properties, such as valley-selective filtering and helicity-resolved functionalities for Dirac fermions. The rich properties and high tunability make SnTe-class materials promising candidates for novel quantum devices.
Low specific contact resistivity to graphene achieved by AuGe/Ni/Au and annealing process
Metal-enhanced fluorescence of graphene oxide by palladium nanoparticles in the blue-green part of the spectrum
Bolometric effect in a waveguide-integrated graphene photodetector
Graphene is an alternative material for photodetectors owing to its unique properties. These include its uniform absorption of light from ultraviolet to infrared and its ultrahigh mobility for both electrons and holes. Unfortunately, due to the low absorption of light, the photoresponsivity of graphene-based photodetectors is usually low, only a few milliamps per watt. In this letter, we fabricate a waveguide-integrated graphene photodetector. A photoresponsivity exceeding 0.11 A·W-1 is obtained which enables most optoelectronic applications. The dominating mechanism of photoresponse is investigated and is attributed to the photo-induced bolometric effect. Theoretical calculation shows that the bolometric photoresponsivity is 4.6 A·W-1. The absorption coefficient of the device is estimated to be 0.27 dB·μ-1.
Large single crystal diamond grown in FeNiMnCo-S-C system under high pressure and high temperature conditions
Large scale fabrication of nitrogen vacancy-embedded diamond nanostructures for single-photon source applications Hot!
Color centers in diamond are prominent candidates for generating and manipulating quantum states of light, even at room temperature. However, the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, we fabricated arrays of diamond nanostructures, differing in both diameter and top end shape, with HSQ, PMMA, and Cr as the etching mask materials, aiming toward large scale fabrication of single-photon sources with enhanced collection efficiency made of nitrogen vacancy (NV) embedded diamond. With a mixture of O2 and CHF3 gas plasma, diamond pillars with diameters down to 45 nm were obtained. The top end shape evolution has been represented with a simple model. The tests of size dependent single-photon properties confirmed an improved single-photon collection efficiency enhancement, larger than tenfold, and a mild decrease of decoherence time with decreasing pillar diameter was observed as expected. These results provide useful information for future applications of nanostructured diamond as a single-photon source.
High performance photodetectors based on high quality InP nanowires Hot!
In this paper, small diameter InP nanowires with high crystal quality were synthesized through a chemical vapor deposition method. Benefitting from the high crystallinity and large specific surface area of InP nanowires, the simply constructed photodetector demonstrates a high responsivity of up to 1170 A·W-1 and an external quantum efficiency of 2.8×105% with a fast rise time of 110 ms and a fall time of 130 ms, even at low bias of 0.1 V. The effect of back-gate voltage on photoresponse of the device was systematically investigated, confirming that the photocurrent dominates over thermionic and tunneling currents in the whole operation. A mechanism based on energy band theory at the junction between metal and semiconductor was proposed to explain the back-gate voltage dependent performance of the photodetectors. These convincing results indicate that fine InP nanowires will have a brilliant future in smart optoelectronics.
Block copolymer morphologies confined by square-shaped particle: Hard and soft confinement
Polydisperse spherical colloidal silica particles: Preparation and application
Parasitic effects of air-gap through-silicon vias in high-speed three-dimensional integrated circuits
An ultra-wideband pattern reconfigurable antenna based on graphene coating
Theoretical investigation of frequency characteristics of free oscillation and injection-locked magnetrons
Analytical threshold voltage model for strained silicon GAA-TFET
Equivalent distributed capacitance model of oxide traps onfrequency dispersion of C-V curve for MOS capacitors
Ultra-low temperature radio-frequency performance of partially depleted silicon-on-insulator n-type metal-oxide-semiconductor field-effect transistors with tunnel diode body contact structures
Radio-frequency (RF) characteristics under ultra-low temperature of multi-finger partially depleted silicon-on-insulator (PD SOI) n-type metal-oxide-semiconductor field-effect transistors (nMOSFETs) with tunnel diode body-contact (TDBC) structure and T-gate body-contact (TB) structure are investigated in this paper. When operating at 77 K, TDBC device suppresses floating-body effect (FBE) as well as the TB device. For TB device and TDBC device, cut-off frequency (fT) improves as the temperature decreases to liquid-helium temperature (77 K) while that of the maximum oscillation frequency (fMAX) is opposite due to the decrease of the unilateral power gain. While operating under 77 K, fT and fMAX of TDBC device reach to 125 GHz and 77 GHz, representing 8% and 15% improvements compared with those of TB device, respectively, which is mainly due to the lower parasitic resistances and capacitances. The results indicate that TDBC SOI MOSFETs could be considered as promising candidates for analog and RF applications over a wide range of temperatures and there is immense potential for the development of RF CMOS integrated circuits for cryogenic applications.
Technology demonstration of a novel poly-Si nanowire thin film transistor
A simple process flow method for the fabrication of poly-Si nanowire thin film transistors (NW-TFTs) without advanced lithographic tools is introduced in this paper. The cross section of the nanowire channel was manipulated to have a parallelogram shape by combining a two-step etching process and a spacer formation technique. The electrical and temperature characteristics of the developed NW-TFTs are measured in detail and compared with those of conventional planar TFTs (used as a control). The as-demonstrated NW-TFT exhibits a small subthreshold swing (191 mV/dec), a high ON/OFF ratio (8.5×107), a low threshold voltage (1.12 V), a decreased OFF-state current, and a low drain-induced-barrier lowering value (70.11 mV/V). The effective trap densities both at the interface and grain boundaries are also significantly reduced in the NW-TFT. The results show that all improvements of the NW-TFT originate from the enhanced gate controllability of the multi-gate over the channel.
Bias-dependent timing jitter of 1-GHz sinusoidally gated InGaAs/InP avalanche photodiode
High-performance InGaN/GaN MQW LEDs with Al-doped ZnO transparent conductive layers grown by MOCVD using H2O as an oxidizer
Dynamic instability of collective myosin II motors
Control of epitaxial growth at a-Si: H/c-Si heterointerface by the working pressure in PECVD
Pedestrians' behavior in emergency evacuation: Modeling and simulation
North west cape-induced electron precipitation and theoretical simulation