Utilizing channel reciprocity, time reversal (TR) technique increases the signal-to-noise ratio (SNR) at the receiver with very low transmitter complexity in complex multipath environment. Present research works about TR multiple-input multiple-output (MIMO) communication all focus on the system implementation and network building. The aim of this work is to analyze the influence of antenna coupling on the capacity of wideband TR MIMO system, which is a realistic question in designing a practical communication system. It turns out that antenna coupling stabilizes the capacity in a small variation range with statistical wideband channel response. Meanwhile, antenna coupling only causes a slight detriment to the channel capacity in a wideband TR MIMO system. Comparatively, uncorrelated stochastic channels without coupling exhibit a wider range of random capacity distribution which greatly depends on the statistical channel. The conclusions drawn from information difference entropy theory provide a guideline for designing better high-performance wideband TR MIMO communication systems.

An integral terminal sliding mode controller is proposed in order to control chaos in a rod-type plasma torch system. In this method, a new sliding surface is defined based on a combination of the conventional sliding surface in terminal sliding mode control and a nonlinear function of the integral of the system states. It is assumed that the dynamics of a chaotic system are unknown and also the system is exposed to disturbance and unstructured uncertainty. To achieve a chattering-free and high-speed response for such an unknown system, an adaptive neuro-fuzzy inference system is utilized in the next step to approximate the unknown part of the nonlinear dynamics. Then, the proposed integral terminal sliding mode controller stabilizes the approximated system based on Lyapunov's stability theory. In addition, a Bee algorithm is used to select the coefficients of integral terminal sliding mode controller to improve the performance of the proposed method. Simulation results demonstrate the improvement in the response speed, chattering rejection, transient response, and robustness against uncertainties.

We study the dynamics of the cubic-quintic nonlinear Schrödinger equation by the symplectic method. The behaviors of the equation are discussed with harmonically modulated initial conditions, and the contributions from the quintic term are discussed. We observe the elliptic orbit, homoclinic orbit crossing, quasirecurrence, and stochastic motion with different nonlinear parameters in this system. Numerical simulations show that the changing processes of the motion of the system and the trajectories in the phase space are various for different cubic nonlinear parameters with the increase of the quintic nonlinear parameter.

Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H=q(J_{x}^{2}+χJ_{y}^{2})+ω_{0}J_{z} in two cavities. This realized Hamiltonian has a distinct property that all parameters can be tuned independently. For proper parameters, the well-studied one- and two-axis twisting Hamiltonians are recovered, and the scaling of N^{-1} of the maximal squeezing factor can occur naturally. On the other hand, in the two-axis twisting Hamiltonian, spin squeezing is usually reduced when increasing the atomic resonant frequency ω_{0}. Surprisingly, we find that by combining with the dimensionless parameter χ(>-1), this atomic resonant frequency ω_{0} can enhance spin squeezing greatly. These results are beneficial for achieving the required spin squeezing in experiments.

Calculations of the quantum information entropy have been extended to a non-analytically solvable situation. Specifically, we have investigated the information entropy for a one-dimensional system with a schematic “Landau” potential in a numerical way. Particularly, it is found that the phase transitional behavior of the system can be well expressed by the evolution of quantum information entropy. The calculated results also indicate that the position entropy S_{x} and the momentum entropy S_{p} at the critical point of phase transition may vary with the mass parameter M but their sum remains as a constant independent of M for a given excited state. In addition, the entropy uncertainty relation is proven to be robust during the whole process of the phase transition.

As is known to all, the electron scattering in classical electromagnetic potential is one of the most widespread applications of quantum theory. Nevertheless, many discussions about electron scattering are based upon single-particle Schrodinger equation or Dirac equation in quantum mechanics rather than the method of quantum field theory. In this paper, by using the path integral approach of quantum field theory, we perturbatively evaluate the scattering amplitude up to the second order for the electron scattering by the classical electromagnetic potential. The results we derive are convenient to apply to all sorts of potential forms. Furthermore, by means of the obtained results, we give explicit calculations for the one-dimensional electric potential.

This paper proposes a well-performing hybrid-type truly quantum random number generator based on the time interval between two independent single-photon detection signals, which is practical and intuitive, and generates the initial random number sources from a combination of multiple existing random number sources. A time-to-amplitude converter and multichannel analyzer are used for qualitative analysis to demonstrate that each and every step is random. Furthermore, a carefully designed data acquisition system is used to obtain a high-quality random sequence. Our scheme is simple and proves that the random number bit rate can be dramatically increased to satisfy practical requirements.

Multi-hop teleportation has significant value due to long-distance delivery of quantum information. Many studies about multi-hop teleportation are based on Bell pairs, partially entangled pairs or W state. The possibility of multi-hop teleportation constituted by partially entangled pairs relates to the number of nodes. The possibility of multi-hop teleportation constituted by double W states is (4/9)^{n} after n-hop teleportation. In this paper, a multi-hop teleportation scheme based on W state and EPR pairs is presented and proved. The successful possibility of quantum information transmitted hop by hop through intermediate nodes is deduced. The possibility of successful transmission is (2/3)^{n} after n-hop teleportation.

A tetrad field that is homogeneous and anisotropic which contains two unknown functions A(t) and B(t) of cosmic time is applied to the field equations of f(t), where T is the torsion scalar, T=T^{μ}_{νρ}S_{μ}^{νρ}. We calculate the equation of continuity and rewrite it as a product of two brackets, the first is a function of f(t) and the second is a function of the two unknowns A(t) and B(t). We use two different relations between the two unknown functions A(t) and B(t) in the second bracket to solve it. Both of these relations give constant scalar torsion and solutions coincide with the de Sitter one. So, another assumption related to the contents of the matter fields is postulated. This assumption enables us to drive a solution with a non-constant value of the scalar torsion and a form of f(t) which represents ΛCDM.

Frozen state from jammed state is one of the most interesting aspects produced when simulating the multidirectional pedestrian flow of high density crowds. Cases of real life situations for such a phenomenon are not exhaustively treated. Our observations in the Hajj crowd show that freezing transition does not occur very often. On the contrary, penetrating a jammed crowd is a common aspect. We believe the kindness of pedestrians facing others whose walking is blocked is a main factor in eliminating the frozen state as well as in relieving the jammed state. We refine the social force model by incorporating a new social force to enable the simulated pedestrians to mimic the real behavior observed in the Hajj area. Simulations are performed to validate the work qualitatively.

The tangent linear (TL) models and adjoint (AD) models have brought great difficulties for the development of variational data assimilation system. It might be impossible to develop them perfectly without great efforts, either by hand, or by automatic differentiation tools. In order to break these limitations, a new data assimilation system, dual-number data assimilation system (DNDAS), is designed based on the dual-number automatic differentiation principles. We investigate the performance of DNDAS with two different optimization schemes and subsequently give a discussion on whether DNDAS is appropriate for high-dimensional forecast models. The new data assimilation system can avoid the complicated reverse integration of the adjoint model, and it only needs the forward integration in the dual-number space to obtain the cost function and its gradient vector concurrently. To verify the correctness and effectiveness of DNDAS, we implemented DNDAS on a simple ordinary differential model and the Lorenz-63 model with different optimization methods. We then concentrate on the adaptability of DNDAS to the Lorenz-96 model with high-dimensional state variables. The results indicate that whether the system is simple or nonlinear, DNDAS can accurately reconstruct the initial condition for the forecast model and has a strong anti-noise characteristic. Given adequate computing resource, the quasi-Newton optimization method performs better than the conjugate gradient method in DNDAS.

This paper aims at developing a novel method of constructing a class of multi-wing chaotic and hyperchaotic system by introducing a unified step function. In order to overcome the essential difficulties in iteratively adjusting multiple parameters of conventional multi-parameter control, this paper introduces a unified step function controlled by a single parameter for constructing various multi-wing chaotic and hyperchaotic systems. In particular, to the best of the authors' knowledge, this is also the first time to find a non-equilibrium multi-wing hyperchaotic system by means of the unified step function control. According to the heteroclinic loop Shilnikov theorem, some properties for multi-wing attractors and its chaos mechanism are further discussed and analyzed. A circuit for multi-wing systems is designed and implemented for demonstration, which verifies the effectiveness of the proposed approach.

A rectangular m×n resistor network with an arbitrary boundary is investigated, and a general resistance formula between two nodes on an arbitrary axis is derived by the Recursion-Transform (RT) method, a problem that has never been resolved before, for the Green's function technique and the Laplacian matrix approach are inapplicable to it. To have the exact solution of resistance is important but it is difficult to obtain under the condition of arbitrary boundary. Our result is directly expressed in a single summation and mainly composed of characteristic roots, which contain both finite and infinite cases. Further, the current distribution is given explicitly as a byproduct of the method. Our framework can be effectively applied to RLC networks. As an application to the LC network, we find that our formulation leads to the occurrence of resonances at h_{1} = 1-cosφ_{i}-sinφ_{i}cotnφ_{i}. This somewhat curious result suggests the possibility of practical applications of our formulae to resonant circuits.

A delayed chasing model is proposed to simulate the chase behavior in the queue, where each member regards the closest one ahead as the target, and the leader is attracted to a target point with slight fluctuation. When the initial distances between neighbors possess an identical low value, the fluctuating target of the leader can cause an amplified disturbance in the queue. After a long period of time, the queue recovers the stable state from the disturbance, forming a straight-line-like pattern again, but distances between neighbors grow. Whether the queue can keep stable or not depends on initial distance, desired velocity, and relaxation time. Furthermore, we carry out convergence analysis to explain the divergence transformation behavior and confirm the convergence conditions, which is in approximate agreement with simulations.

Atmospheric concentrations of radon (^{222}Rn) gas and its short-lived progenies ^{218}Po, ^{214}Pb, and ^{214}Po were continuously monitored every four hours at the ground level in Jeddah city, Kingdom of Saudi Arabia. The measurements were performed three times every week, starting from November 2014 to October 2015. A method of electrostatic precipitation of positively charged ^{218}Po and ^{214}Po by a positive voltage was applied for determining ^{222}Rn gas concentration. The short-lived ^{222}Rn progeny concentration was determined by using a filter holder connected with the alpha-spectrometric technique. The meteorological parameters (relative air humidity, air temperature, and wind speed) were determined during the measurements of ^{222}Rn and its progeny concentrations. ^{222}Rn gas as well as its short-lived progeny concentration display a daily and seasonal variation with high values in the night and early morning hours as compared to low values at noon and in the afternoon. The observed monthly atmospheric concentrations showed a seasonal trend with the highest values in the autumn/winter season and the lowest values in the spring/summer season. Moreover, and in parallel with alpha-spectrometric measurements, a single filter-holder was used to collect air samples. The deposited activities of ^{214}Pb and the long-lived ^{222}Rn daughter ^{210}Pb on the filter were measured with the gamma spectrometric technique. The measured activity concentrations of ^{214}Pb by both techniques were found to be relatively equal largely. The highest mean seasonally activity concentrations of ^{210}Pb were observed in the autumn/winter season while the lowest mean were observed in the spring/summer season. The mean residence time (MRT) of aerosol particles in the atmospheric air could be estimated from the activity ratios of ^{210}Pb/^{214}Pb.

A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS_{2} by fitting the accurate ab initio energies, which are calculated at the multireference configuration interaction level with the aug-cc-pV QZ basis set. By using the double many-body expansion-scaled external correlation method, such calculated ab initio energies are then slightly corrected by scaling their dynamical correlation. A grid of 2767 ab initio energies is used in the least-square fitting procedure with the total root-mean square deviation being 1.406 kcal· mol^{-1}. The topographical features of the HS_{2}(A^{2}A') global potential energy surface are examined in detail. The attributes of the stationary points are presented and compared with the corresponding ab initio results as well as experimental and other theoretical data, showing good agreement. The resulting potential energy surface of HS_{2}(A^{2}A') can be used as a building block for constructing the global potential energy surfaces of larger m S/H molecular systems and recommended for dynamic studies on the title molecular system.

By performing the electronic structure computation of a Si atom, we compare two iteration algorithms of Broyden electron density mixing in the literature. One was proposed by Johnson and implemented in the well-known VASP code. The other was given by Eyert. We solve the Kohn-Sham equation by using a conventional outward/inward integration of the differential equation and then connect two parts of solutions at the classical turning points, which is different from the method of the matrix eigenvalue solution as used in the VASP code. Compared to Johnson's algorithm, the one proposed by Eyert needs fewer total iteration numbers.

We present a laser frequency locking to Rydberg transition with electromagnetically induced transparency (EIT) spectra in a room-temperature cesium vapor cell. Cesium levels 6S_{1/2}, 6P_{3/2}, and the nD_{5/2} state, compose a cascade three-level system, where a coupling laser drives Rydberg transition, and probe laser detects the EIT signal. The error signal, obtained by demodulating the EIT signal, is used to lock the coupling laser frequency to Rydberg transition. The laser frequency fluctuation, ~0.7 MHz, is obtained after locking on, with the minimum Allan variance to be 8.9× 10^{-11}. This kind of locking method can be used to stabilize the laser frequency to the excited transition.

The spatial distribution in high-order harmonic generation (HHG) from the asymmetric diatomic molecule HeH^{2+} is investigated by numerically solving the non-Born-Oppenheimer time-dependent Schrödinger equation (TDSE). The spatial distribution of the HHG spectra shows that there is little contribution in HHG around the geometric center of two nuclei (z = 1.17 a.u.) and the equilibrium internuclear position of the H nucleus (z = 3.11 a.u.). We demonstrate the carrier envelope phase (CEP) effect on the spatial distribution of HHG in a few-cycle laser pulse. The HHG process is investigated by the time evolution of the electronic density distribution. The time-frequency analysis of HHG from two nuclei in HeH^{2+} is presented to further explain the underlying physical mechanism.

We investigate the plasmonic-field-enhanced high-order harmonic generation (HHG) of H atom driven by few-cycle laser pulses, by solving the time-dependent Schrödinger equation (TDSE). Compared with the homogeneous field, HHG spectra generated by inhomogeneous field exhibit two-plateau structure. We analyze the origin of the two plateaus by using the semiclassical trajectory method. Our results from both classical and TDSE simulations show that the cutoffs of the two plateaus are dramatically affected by the carrier-envelope phase (CEP) of laser pulse in the inhomogeneous field, even for a little longer pulse. Thus, we can determine the CEP of driving laser based on the cutoff position of HHG generated in the inhomogeneous field.

We experimentally demonstrate the Coulomb explosion process of CS_{2} molecule under a near-infrared (800 nm) intense femtosecond laser field by a DC-sliced ion imaging technique. We obtain the DC-sliced images of these fragment ions S^{+}, S^{2+}, CS^{+}, and CS^{2+} by breaking one C-S bond, and assign their Coulomb explosion channels by considering their kinetic energy release and angular distribution. We also numerically simulate the dissociation dynamics of parent ions CS_{2}^{k+} (k=2-4) by a Coulomb potential approximation, and obtain the time evolution of Coulomb energy and kinetic energy release, which indicates that the dissociation time of parent ions CS_{2}^{k+} decreases with the increase of the charge number k. These experimental and theoretical results can serve as a useful benchmark for those researchers who work in the related area.

Alloy nanoparticles exhibit higher catalytic activity than monometallic nanoparticles, and their stable structures are of importance to their applications. We employ the simulated annealing algorithm to systematically explore the stable structure and segregation behavior of tetrahexahedral Pt-Pd-Cu-Au quaternary alloy nanoparticles. Three alloy nanoparticles consisting of 443 atoms, 1417 atoms, and 3285 atoms are considered and compared. The preferred positions of atoms in the nanoparticles are analyzed. The simulation results reveal that Cu and Au atoms tend to occupy the surface, Pt atoms preferentially occupy the middle layers, and Pd atoms tend to segregate to the inner layers. Furthermore, Au atoms present stronger surface segregation than Cu ones. This study provides a fundamental understanding on the structural features and segregation phenomena of multi-metallic nanoparticles.

Realizing a molecular magneto-optical trap has been a dream for cold molecular physicists for a long time. However, due to the complex energy levels and the small effective Lande g-factor of the excited states, the traditional magneto-optical trap (MOT) scheme does not work very well for polar molecules. One way to overcome this problem is the switching MOT, which requires very fast switching of both the magnetic field and the laser polarizations. Switching laser polarizations is relatively easy, but fast switching of the magnetic field is experimentally challenging. Here we propose an alternative approach, the microwave-mediated MOT, which requires a slight change of the current experimental setup to solve the problem. We calculate the MOT force and compare it with the traditional MOT and the switching MOT scheme. The results show that we can operate a good MOT with this simple setup.

SPECIAL TOPIC—Soft matter and biological physics (Review)

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Visible light variable optical attenuators (VOA) are essential devices in the application of channel power regulation and equalization in wavelength-division multiplexing cross-connect nodes in plastic optical fiber (POF) transmission systems. In this paper, a polymer/silica hybrid waveguide thermo-optic attenuator based on multimode interference (MMI) coupler is designed and fabricated to operate at 650 nm. The single-mode transmission condition, MMI coupler, and transition taper dimensions are optimized through the beam propagation method. Thermal analysis based on material properties provides the optimized heater placement angle. The fabricated VOA presents an attenuation of 26.5 dB with a 21-mW electrical input power at 650 nm. The rise time and fall time are 51.99 and 192 μs, respectively. The time-stability measurement results prove its working reliability.

The dynamics of the compressed electron layer (CEL) are investigated when a linearly polarized (LP) laser pulse irradiates a plasma target. The turbulent motion of the CEL is investigated by a simple model, which is verified by particle-in-cell (PIC) simulations. It is found that the compressed layer disperses in a few cycles of the laser duration, because the CEL comes back with a large velocity in the opposite direction of the laser incident. A larger wavelength laser can be used to tailor the proton beam by reducing the turbulence of the CEL in the region of the LP laser acceleration.

A novel image encryption method based on the random sequence generated from the generalized information domain and permutation-diffusion architecture is proposed. The random sequence is generated by reconstruction from the generalized information file and discrete trajectory extraction from the data stream. The trajectory address sequence is used to generate a P-box to shuffle the plain image while random sequences are treated as keystreams. A new factor called drift factor is employed to accelerate and enhance the performance of the random sequence generator. An initial value is introduced to make the encryption method an approximately one-time pad. Experimental results show that the random sequences pass the NIST statistical test with a high ratio and extensive analysis demonstrates that the new encryption scheme has superior security.

We explore two observable nonclassical properties of quantum states generated by repeatedly operating annihilation-then-creation (AC) and creation-then-annihilation (CA) on the coherent state, respectively, such as higher-order sub-Poissonian statistics and higher-order squeezing-enhanced effect. The corresponding analytical expressions are derived in detail depending on m. By numerically comparing those quantum properties, it is found that these states above have very different nonclassical properties and nonclassicality is exhibited more strongly after AC operation than after CA operation.

We theoretically investigate the optomechanical induced transparency (OMIT) phenomenon in a two-cavity system which is composed of two optomechanical cavities. Both of the cavities consist of a fixed mirror and a high-Q mechanical resonator, and they couple to each other via a common waveguide. We show that in the presence of a strong pump field applied to one cavity and a weak probe field applied to the other, a triple-OMIT can be observed in the output field at the probe frequency. The two mechanical resonators in the two cavities are identical, but they lead to different quantum interference pathways. The transparency windows are induced by the coupling of the two cavities and the optical pressure radiated to the mechanical resonators, which can be controlled via the power of the pump field and the coupling strength of the two cavities.

We theoretically investigate the tunable delay and advancement of microwave signals based on bichromatic electromechanically induced transparency in a three-mode circuit electromechanical system, where two nanomechanical resonators with closely spaced frequencies are independently coupled to a common microwave cavity. In the presence of a strong microwave pump field, we obtain two transparency windows accompanied by steep phase dispersion in the transmitted microwave probe field. The width of the transparency window and the group delay of the probe field can be controlled effectively by the power of the pump field. It is shown that the maximum group delay of 0.12 ms and the advancement of 0.27 ms can be obtained in the current experiments.

Pumped by a 940 nm fiber-coupled diode laser, a passively mode-locked Yb:YAG thin disk oscillator was demonstrated with a semiconductor saturable absorber mirror (SESAM). 12.1 W mode-locked pulses were obtained with pulse duration of 698 fs at the repetition rate of 57.43 MHz. Measurement showed that the beam quality was close to the diffraction limit.

In pulsed laser drilling, melt ejection greatly influences the keyhole shape and its quality as well, but its mechanism has not been well understood. In this paper, numerical simulation and experimental investigations based on 304 stainless steel and aluminum targets are performed to study the effects of material parameters on melt ejection. The numerical method is employed to predict the temperatures, velocity fields in the solid, liquid, and vapour front, and melt pool dynamics of targets as well. The experimental methods include the shadow-graphic technique, weight method, and optical microscope imaging, which are applied to real-time observations of melt ejection phenomena, measurements of collected melt and changes of target mass, observations of surface morphology and the cross-section of the keyhole, respectively. Numerical and experimental results show that the metallic material with high thermal diffusivity like aluminum is prone to have a thick liquid zone and a large quantity of melt ejection. Additionally, to the best of our knowledge, the liquid zone is used to illustrate the relations between melt ejection and material thermal diffusivity for the first time. The research result in this paper is useful for manufacturing optimization and quality control in laser-material interaction.

Femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS) is a versatile technique with advantages of high sensitivity, broad detection bandwidth, and intrinsic spectrum correction function. These advantages should benefit the study of coherent emission, such as measurement of lasing dynamics. In this letter, the FNOPAS was used to trace the lasing process in Rhodamine 6G (R6G) solution and organic semiconductor nano-wires. High-quality transient emission spectra and lasing dynamic traces were acquired, which demonstrates the applicability of FNOPAS in the study of lasing dynamics. Our work extends the application scope of the FNOPAS technique.

We proposed a new model for controlling the optical bistability (OB) and optical multistability (OM) in a defect slab doped with four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al_{0.3} Ga_{0.7}As barriers. The effects of biexciton energy renormalization, exciton spin relaxation, and thickness of the slab on the OB and OM properties of the defect slab were theoretically investigated. We found that the transition from OB to OM or vice versa is possible by adjusting the controllable parameters in a lab. Moreover, the transmission, reflection, and absorption properties of the weak probe light through the slab were also discussed in detail.

Spectral diagnosis of radiation from laser plasma interaction and monochromation of radiation source are hot and important topics recently. Grating is one of the primary optical elements to do this job. Although easy to fabricate, traditional diffraction grating suffers from multi-order diffraction contamination. On the other hand, sinusoidal amplitude grating has the nonharmonic diffraction property, but it is too difficult to fabricate, especially for x-ray application. A novel nonharmonic diffraction grating named random position rectangle grating (RPRG) is proposed in this paper. Theoretical analysis and experiment results show that the RPRG is both higher order diffraction suppressing and not difficult to fabricate. Additionally, it is highly efficient; its first order absolute theoretical diffraction efficiency reaches 4.1%. Our result shows that RPRG is a novel tool for radiation diagnosis and monochromation.

The effects of the micro-ramps on supersonic turbulent flow over a forward-facing step (FFS) was experimentally investigated in a supersonic low-noise wind tunnel at Mach number 3 using nano-tracer planar laser scattering (NPLS) and particle image velocimetry (PIV) techniques. High spatiotemporal resolution images and velocity fields of supersonic flow over the testing model were captured. The fine structures and their spatial evolutionary characteristics without and with the micro-ramps were revealed and compared. The large-scale structures generated by the micro-ramps can survive the downstream FFS flowfield. The micro-ramps control on the flow separation and the separation shock unsteadiness was investigated by PIV results. With the micro-ramps, the reduction in the range of the reversal flow zone in streamwise direction is 50% and the turbulence intensity is also reduced. Moreover, the reduction in the average separated region and in separation shock unsteadiness are 47% and 26%, respectively. The results indicate that the micro-ramps are effective in reducing the flow separation and the separation shock unsteadiness.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Raman spectra of C_{60} filled single-walled carbon nanotubes (C_{60}@SWNTs) with diameters of 1.3-1.5 nm have been studied under high pressure. A plateau in the pressure dependence of the G-band frequency at around 10 GPa was observed in both experiments with 514 nm and 830 nm excitation lasers, which is similar to the high pressure behaviors of pristine SWNTs. This structural transition has been assigned to the transformation into a peanut-like structure of the nanotubes. At pressure below 2 GPa, no obvious Raman signature related to the structural transition of nanotubes was observed, unlike what has been reported for C_{70} filled nanotubes. We discussed this point in terms of the arrangement differences of C_{60} and C_{70} molecules inside the nanotubes. At higher pressure up to 15 GPa, a graphite-like pressure evolution was observed in our C_{60}@SWNTs.

Based on the density functional theory, we calculated the structures of the two main possible self-interstitial atoms (SIAs) as well as the migration energy of tungsten (W) atoms. It was found that the difference of the (110) and (111) formation energies is 0.05-0.3 eV. Further analysis indicated that the stability of SIAs is closely related to the concentration of the defect. When the concentration of the point defect is high, (110) SIAs are more likely to exist, (111) SIAs are the opposite. In addition, the vacancy migration probability and self-recovery zones for these SIAs were researched by making a detailed comparison. The calculation provided a new viewpoint about the stability of point defects for self-interstitial configurations and would benefit the understanding of the control mechanism of defect behavior for this novel fusion material.

We study the effect of pressure on electronic and thermoelectric properties of Mg_{2}}Si using the density functional theory and Boltzmann transport equations. The variation of lattice constant, band gap, bulk modulus with pressure is also analyzed. Further, the thermoelectric properties (Seebeck coefficient, electrical conductivity, electronic thermal conductivity) have been studied as a function of temperature and pressure up to 1200 K. The results show that Mg_{2}Si is an n-type semiconductor with a band gap of 0.21 eV. The negative value of the Seebeck coefficient at all pressures indicates that the conduction is due to electrons. With the increase in pressure, the Seebeck coefficient decreases and electrical conductivity increases. It is also seen that, there is practically no effect of pressure on the electronic contribution of thermal conductivity. The paper describes the calculation of the lattice thermal conductivity and figure of merit of Mg_{2}}Si at zero pressure. The maximum value of figure of merit is attained 1.83×10^{-3} at 1000 K. The obtained results are in good agreement with the available experimental and theoretical results.

Three-dimensional (3D) crossbar array architecture is one of the leading candidates for future ultra-high density nonvolatile memory applications. To realize the technological potential, understanding the reliability mechanisms of the 3D RRAM array has become a field of intense research. In this work, the endurance performance of the 3D 1D1R crossbar array under the thermal effect is investigated in terms of numerical simulation. It is revealed that the endurance performance of the 3D 1D1R array would be seriously deteriorated under thermal effects as the feature size scales down to a relatively small value. A possible method to alleviate the thermal effects is provided and verified by numerical simulation.

The thermodynamic properties of an InSb quantum dot have been investigated in the presence of Rashba spin-orbit interaction and a static magnetic field. The energy spectrum and wave-functions for the system are obtained by solving the Schrodinger wave-equation analytically. These energy levels are employed to calculate the specific heat, entropy, magnetization and susceptibility of the quantum dot system using canonical formalism. It is observed that the system is susceptible to maximum heat absorption at a particular value of magnetic field which depends on the Rashba coupling parameter as well as the temperature. The variation of specific heat shows a Schottky-like anomaly in the low temperature limit and rapidly converges to the value of 2k_{B} with the further increase in temperature. The entropy of the quantum dot is found to be inversely proportional to the magnetic field but has a direct variation with temperature. The substantial effect of Rashba spin-orbit interaction on the magnetic properties of quantum dot is observed at low values of magnetic field and temperature.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

We study the effects of the next-nearest-neighbor hopping and nearest-neighbor interactions on topological phases in a one-dimensional generalized Kitaev model. In the noninteracting case, we define a topological number and calculate exactly the phase diagram of the system. With addition of the next-nearest-neighbor hopping, the change of phase boundary between the topological and trivial regions can be described by an effective shift of the chemical potential. In the interacting case, we obtain the entanglement spectrum, the degeneracies of which correspond to the topological edge modes, by using the infinite time-evolving block decimation method. The results show that the interactions change the phase boundary as adding an effective chemical potential which can be explained by the change of the average number of particles.

The high pressure behaviors of Th_{4}H_{15} and ThH_{2} are investigated by using the first-principles calculations based on the density functional theory (DFT). From the energy-volume relations, the bct phase of ThH_{2} is more stable than the fcc phase at ambient conditions. At high pressure, the bct ThH_{2 } and bcc Th_{4}H_{15} phases are more brittle than they are at ambient pressure from the calculated elastic constants and the Poisson ratio. The thermodynamic stability of the bct phase ThH_{2} is determined from the calculated phonon dispersion. In the pressure domain of interest, the phonon dispersions of bcc Th_{4}H_{15} and bct ThH_{2} are positive, indicating the dynamical stability of these two phases, while the fcc ThH_{2} is unstable. The thermodynamic properties including the lattice vibration energy, entropy, and specific heat are predicted for these stable phases. The vibrational free energy decreases with the increase of the temperature, and the entropy and the heat capacity are proportional to the temperature and inversely proportional to the pressure. As the pressure increases, the resistance to the external pressure is strengthened for Th_{4}H_{15} and ThH_{2}.

Motivated by recent experimental observations of metallic conduction in the quasi-two-dimensional SrFeO_{2}, we study the epitaxial strain effect on the formation and electronic structures of oxygen vacancy (V_{o}) by first-principles calculations. The bulk SrFeO_{2} is found to have the G-type antiferromagnetic ordering (G-AFM) at zero strain, which agrees with the experiment. Under compressive strain the bulk SrFeO_{2} keeps the G-AFM and has the trend of Mott insulator-metal transition. Different from most of the previous similar work about the strain effect on V_{o}, both the tensile strain and the compressive strain enhance the V_{o} formation. It is found that the competitions between the band energies and the electrostatic interactions are the dominant mechanisms in determining the V_{o} formation. We confirm that the V_{o} in SrFeO_{2} would induce the n-type conductivity where the donor levels are occupied by the delocalized d_{x2}-_{y2} electrons. It is suggested that the vanishing of n-type conductivity observed by the Hall measurement on the strained films are caused by the shift of donor levels into the conduction band. These results would provide insightful information for the realization of metallic conduction in SrFeO_{2}.

We investigate magnetic ordering and electronic structures of Cr_{2}MoO_{6} under hydrostatic pressure. To overcome the band gap problem, the modified Becke and Johnson exchange potential is used to investigate the electronic structures of Cr_{2}MoO_{6}. The insulating nature at the experimental crystal structure is produced, with a band gap of 1.04 eV, and the magnetic moment of the Cr atom is 2.50 μ_{B}, compared to an experimental value of about 2.47 μ_{B}. The calculated results show that an antiferromagnetic inter-bilayer coupling-ferromagnetic intra-bilayer coupling to a ferromagnetic inter-bilayer coupling-antiferromagnetic intra-bilayer coupling phase transition is produced with the pressure increasing. The magnetic phase transition is simultaneously accompanied by a semiconductor-metal phase transition. The magnetic phase transition can be explained by the Mo-O hybridization strength, and ferromagnetic coupling between two Cr atoms can be understood by empty Mo-d bands perturbing the nearest O-p orbital.

We have prepared three groups of Ge-As-Se glasses in which the Se content is 5.5 mol%, 10 mol%, and 20 mol% rich, respectively. We explored the possibility of suppressing the formation of the Ge-Ge and As-As homopolar bonds in the glasses. Thermal kinetics analysis indicated that the 5.5 mol% Se-rich Ge_{11.5}As_{24}Se_{64.5} glass exhibits the minimum fragility and thus is most stable against structural relaxation. Analysis of the Raman spectra of the glasses indicated that the Ge-Ge and As-As homopolar bonds could be almost completely suppressed in 20 mol% Se-rich Ge_{15}As_{14}Se_{71} glass.

We have investigated the structural and electronic characteristics of hydrogenated boron-nitride bilayer (H-BNBN-H) using first-principles calculations. The results show that hydrogenation can significantly reduce the energy gap of the BN-BN into the visible-light region. Interestingly, the electric field induced by the interface dipoles helps to promote the formation of well-separated electron-hole pairs, as demonstrated by the charge distribution of the VBM and CBM. Moreover, the applied bias voltage on the vertical direction of the bilayer could modulate the band gap, resulting in transition from semiconductor to metal. We conclude that H-BNBN-H could improve the solar energy conversion efficiency, which may provide a new way for tuning the electronic devices to meet different environments and demands.

We studied the interface electronic and magnetic properties of Fe/Co deposited on Au substrate and researched the effects of roughness at the interfaces within augmented space formalism (ASF). The full calculation is carried out by recursion and tight-binding linear muffin tin orbital (TB-LMTO) methods. The amount of roughness is different at different atomic layers. The formalism is also applied to sharp interface, when interdiffusion of atoms is negligible. Our results of one monolayer transition metal agree with other reported results. A realistic rough interface is also modeled with three and four monolayers of transition metals, deposited on Au substrates.

A gold dimer structure consisting of a notched triangle nanoslice and a rectangle nanorod is proposed to produce distinct Fano resonance. Owing to the coupling between the dipole plasmon mode of the nanorod and the dipole or quadrupole plasmon mode of the nanoslice, the extinction spectrum with a deep Fano dip is formed and can be well fitted by the Fano interference model for different geometry parameters. In addition, Fano resonance of the gold dimer nanostructure also intensely depends on the polarization direction of incident light. Moreover, Fano resonance of the triangle-rod trimer is also analyzed by adding another nanorod into the former dimer and exhibits the splitting of plasmonic resonant peak in high order coupling modes. The plasmonic hybridizations in these nanostructures have been analyzed for revealing the physical origin of the Fano resonance.

High-performance Ge n^{+}/p junctions were fabricated at a low formation temperature from 325℃ to 400℃ with a metal(nickel)-induced dopant activation technique. The obtained NiGe electroded Ge n^{+}/p junction has a rectification ratio of 5.6×10^{4} and a forward current of 387 A/cm^{2} at -1 V bias. The Ni-based metal-induced dopant activation technique is expected to meet the requirement of the shallow junction of Ge MOSFET.

Highly textured Heusler alloy Mn_{46}Ni_{42}Sn_{11}Sb_{1} ribbons were prepared by melt spinning. The annealed high Mn content Mn_{46}Ni_{42}Sn_{11}Sb_{1} ribbon cross-section microstructure, crystal structure, martensitic transformation (MT), and magnetoresistance (MR) properties were investigated. The MR in the annealed ribbon was assessed by the magnetic field direction perpendicular to the ribbon surface with the magnetic field up to 30 kOe. The large negative value of 25% for MR was obtained at 244 K. The exchange bias (EB) effects of the as-spun and annealed ribbons were investigated. After annealing, the EB effects have been improved by about 25 Oe at the temperature of 50 K. The magnetizations have increased approximately by 10% more than the as-spun ribbon.

In this work, a method based on scanning Kelvin probe microscopy is proposed to separately extract source/drain (S/D) series resistance in operating amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors. The asymmetry behavior of S/D contact resistance is deduced and the underlying physics is discussed. The present results suggest that the asymmetry of S/D contact resistance is caused by the difference in bias conditions of the Schottky-like junction at the contact interface induced by the parasitic reaction between contact metal and a-IGZO. The overall contact resistance should be determined by both the bulk channel resistance of the contact region and the interface properties of the metal-semiconductor junction.

A theoretical study of resonant tunneling is carried out for an inverse parabolic double-barrier structure subjected to an external electric field. Tunneling transmission coefficient and density of states are analyzed by using the non-equilibrium Green's function approach based on the finite difference method. It is found that the resonant peak of the transmission coefficient, being unity for a symmetrical case, reduces under the applied electric field and depends strongly on the variation of the structure parameters.

The rectification ratio of organic magnetic co-oligomer diodes is investigated theoretically by changing the molecular length. The results reveal two distinct length dependences of the rectification ratio: for a short molecular diode, the charge-current rectification changes little with the increase of molecular length, while the spin-current rectification is weakened sharply by the length; for a long molecular diode, both the charge-current and spin-current rectification ratios increase quickly with the length. The two kinds of dependence switch at a specific length accompanied with an inversion of the rectifying direction. The molecular ortibals and spin-resolved transmission analysis indicate that the dominant mechanism of rectification suffers a change at this specific length, that is, from asymmetric shift of molecular eigenlevels to asymmetric spatial localization of wave functions upon the reversal of bias. This work demonstrates a feasible way to control the rectification in organic co-oligomer spin diodes by adjusting the molecular length.

Josephson junction array chips for microvolt applications have been designed and fabricated. A voltage step as small as 1 μV has been observed for a single junction in the array when it is driven by 483.59 MHz microwave. By selecting different parts of the array, it can output a voltage from 1 μV to 256 μV. The flat region of the voltage steps is over 200 μA. This kind of array is useful for potential microvolt applications.

We have studied the angular magnetoresistance of iron pnictides BaFe_{2-x}Ni_{x}As_{2}, which shows clear 180 degree periodicity as fitted by a cosine function. In the x = 0.065 sample, the phase of the two-fold symmetry changes 90 degrees above the tetragonal-to-orthorhombic structural transition temperature T_{s}. Since the phase at low temperature is associated with the rotation of orthorhombic domains by magnetic field, we show that even vacuum grease can push the presence of orthorhombic domains at temperatures much higher than T_{s}. Our results suggest that residual stress may have significant effects in studying the nematic orders and its fluctuations in iron pnictides.

The electronic structures, the effective masses, and optical properties of spinel CdCr_{2}S_{4} are studied by using the full-potential linearized augmented planewave method and a modified Becke-Johnson exchange functional within the density-functional theory. Most importantly, the effects of the spin-orbit coupling (SOC) on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center. SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr_{2}S_{4}. These should be useful to deeply understand spinel CdCr_{2}S_{4} as a ferromagnetic semiconductor for possible semiconductor spintronic applications.

Resource-saving (PrNdCe)_{2}Fe_{14}B sintered magnets with nominal composition (PrNd)_{15-x}Ce_{x}Fe_{77}B_{8} (x=0-10) were prepared using a dual alloy method by mixing (PrNd)_{5}Ce_{10}Fe_{77}B_{8} with (PrNd)_{15}Fe_{77}B_{8} powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in (PrNd)_{11}Ce_{4}Fe_{77}B_{8}, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where PrNd concentration is strongly dependent on the additive amount of (PrNd)_{5}Ce_{10}Fe_{77}B_{8} powders. In addition, for Ce atomic percent of 8%, 7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets.

A phenomenological Landau-Devonshire theory is developed to investigate the ferroelectric, dielectric, and piezoelectric properties of (110) oriented Pb(Zr_{1-x}Ti_{x})O_{3} (x=0.4, 0.5, 0.6, and 0.7) thin films. At room temperature, the tetragonal a_{1} phase, the orthorhombic a_{2}c phase, the triclinic γ_{1} phase, and the triclinic γ_{2} phase are stable. The appearance of the negative polarization component P_{2} in the a_{2}c phase and the γ_{1} phase is attributed to the nonlinear coupling terms in the thermodynamic potential. The γ phase of the Pb(Zr_{1-x}Ti_{x})O_{3} thin films has better dielectric and piezoelectric properties than the a_{2}c phase and the a_{1} phase. The largest dielectric and piezoelectric coefficients are obtained in the Pb(Zr_{0.5}Ti_{0.5})O_{3} thin film. The piezoelectric coefficient of 110-150 pm/V is obtained in the (110) oriented Pb(Zr_{0.5}Ti_{0.5})O_{3} thin film, and the Pb(Zr_{0.3}Ti_{0.7})O_{3} thin film has the remnant polarization and relative dielectric constant of 50 μC/cm^{2} and 100, respectively, which are in agreement with the experimental measurements reported in the literature.

In this paper, the principle of discharge-based pulsed I-V technique is introduced. By using it, the energy and spatial distributions of electron traps within the 4-nm HfO_{2} layer have been extracted. Two peaks are observed, which are located at ΔE~-1.0 eV and -1.43 eV, respectively. It is found that the former one is close to the SiO_{2}/HfO_{2} interface and the latter one is close to the gate electrode. It is also observed that the maximum discharge time has little effect on the energy distribution. Finally, the impact of electrical stress on the HfO_{2} layer is also studied. During stress, no new electron traps and interface states are generated. Meanwhile, the electrical stress also has no impact on the energy and spatial distribution of as-grown traps. The results provide valuable information for theoretical modeling establishment, material assessment, and reliability improvement for advanced semiconductor devices.

We have investigated the electron affinity of Si-doped AlN films (N_{Si}= 1.0 ×10^{18}-1.0×10^{19} cm^{-3}) with thicknesses of 50, 200, and 400 nm, synthesized by metalorganic chemical vapor deposition (MOCVD) under low pressure on the n-type (001)6H-SiC substrates. The positive and small electron affinity of AlN films was observed through the ultraviolet photoelectron spectroscopy (UPS) analysis, where an increase in electron affinity appears with the thickness of AlN films increasing, i.e., 0.36 eV for the 50-nm-thick one, 0.58 eV for the 200-nm-thick one, and 0.97 eV for the 400-nm-thick one. Accompanying the x-ray photoelectron spectroscopy (XPS) analysis on the surface contaminations, it suggests that the difference of electron affinity between our three samples may result from the discrepancy of surface impurity contaminations.

In ferroelectric liquid crystals, phase transitions can be induced by an electric field. The current constant method allows these transition to be quickly localized and thus the (E,T) phase diagram of the studied product can be obtained. In this work, we make a slight modification to the measurement principles based on this method. This modification allows the characteristic parameters of ferroelectric liquid crystal to be quantitatively measured. The use of a current square signal highlights a phenomenon of ferroelectric hysteresis with remnant polarization at null field, which points out an effect of memory in this compound.

Based on the Schrödinger equation for envelope function in the effective mass approximation, linear and nonlinear optical absorption coefficients in a multi-subband lens quantum dot are investigated. The effects of quantum dot size on the interband and intraband transitions energy are also analyzed. The finite element method is used to calculate the eigenvalues and eigenfunctions. Strain and In-mole-fraction effects are also studied, and the results reveal that with the decrease of the In-mole fraction, the amplitudes of linear and nonlinear absorption coefficients increase. The present computed results show that the absorption coefficients of transitions between the first excited states are stronger than those of the ground states. In addition, it has been found that the quantum dot size affects the amplitudes and peak positions of linear and nonlinear absorption coefficients while the incident optical intensity strongly affects the nonlinear absorption coefficients.

Two types of flexible terahertz metamaterials were fabricated on polyethylene naphthalate (PEN) substrates. The unit cell of one type consists of two identical split-ring resonators (SRRs) that are arranged face-to-face (i.e., FlexMetaF); the unit cell of the other type has nothing different but is arranged back-to-back (i.e., FlexMetaB). FlexMetaF and FlexMetaB illustrate the similar transmission dips under zero strain because the excitation of fundamental inductive-capacitive (LC) resonance is mainly dependent on the geometric structure of individual SRR. However, if a gradually variant strain is applied to bend FlexMetaF and FlexMetaB, the new resonant peaks appear: in the case of FlexMetaF, the peaks are located at the lower frequencies; in the case of FlexMetaB, the peaks appear at the frequencies adjacent to the LC resonance. The origin and evolution of strain-induced resonances are studied. The origin is ascribed to the detuning effect and the different responses to strain from FlexMetaF and FlexMetaB are associated with the coupling effect. These findings may improve the understanding on flexible terahertz metamaterials and benefit their applications in flexible or curved devices.

Graphene decorated nanomaterials and nanostructures can potentially be used in military and medical science applications. In this article, we study the optical properties of a graphene wrapping silica core-shell spherical nanoparticle under illumination of external light by using the Mie theory. We find that the nanoparticle can exhibit surface plasmon resonance (SPR) that can be broadly tuned from mid infrared to near infrared via simply changing the geometric parameters. A simplified equivalent dielectric permittivity model is developed to better understand the physics of SPR, and the calculation results agree well qualitatively with the rigorous Mie theory. Both calculations suggest that a small radius of graphene wrapping nanoparticle with high Fermi level could move the SPR wavelength of graphene into the near infrared regime.

Band structure, electron distribution, direct-bandgap light emission, and optical gain of tensile strained, n-doped Ge at different temperatures were calculated. We found that the heating effects not only increase the electron occupancy rate in the Γ valley of Ge by thermal excitation, but also reduce the energy difference between its Γ valley and L valley. However, the light emission enhancement of Ge induced by the heating effects is weakened with increasing tensile strain and n-doping concentration. This phenomenon could be explained by that Ge is more similar to a direct bandgap material under tensile strain and n-doping. The heating effects also increase the optical gain of tensile strained, n-doped Ge at low temperature, but decrease it at high temperature. At high temperature, the hole and electron distributions become more flat, which prevent obtaining higher optical gain. Meanwhile, the heating effects also increase the free-carrier absorption. Therefore, to obtain a higher net maximum gain, the tensile strained, n-doped Ge films on Si should balance the gain increased by the heating effects and the optical loss induced by the free-carrier absorption.

We present an infrared spectroscopy study of charge dynamics in CaCo_{2}As_{2} single crystal. In this material, the optical conductivity can be described by two Drude components with different scattering rates (1/τ): a broad incoherent background and a narrow Drude component. By monitoring the temperature dependence, we find that only the narrow Drude component is temperature-dependent and determines the transport properties. Especially a Fermi liquid behavior of carriers is revealed by the T^{2} behavior in the dc resistivity ρ_{n} and scattering rate 1/τ_{n}, indicating a coherent nature of quasiparticles in the narrow Drude subsystem.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

The effects of Mg doping in the quantum barriers (QBs) on the efficiency droop of GaN based light emitting diodes (LEDs) were investigated through a duel wavelength method. Barrier Mg doping would lead to the enhanced hole transportation and reduced polarization field in the quantum wells (QWs), both may reduce the efficiency droop. However, heavy Mg doping in the QBs would strongly deteriorate the crystal quality of the QWs grown after the doped QB. When increasing the injection current, the carriers would escape from the QWs between n-GaN and the doped QB and recombine non-radiatively in the QWs grown after the doped QB, leading to a serious efficiency droop.

The structural, electronic, and magnetic properties of double perovskite Sr_{2}FeReO_{6} containing eight different imperfections of Fe_{Re} or Re_{Fe} antisites, Fe1-Re1 or Fe1-Re4 interchanges, V_{Fe}, V_{Re}, V_{O} or V_{Sr} vacancies have been studied by using the first-principles projector augmented wave (PAW) within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction (GGA+U). No obvious structural changes are observed for the imperfect Sr_{2}FeReO_{6} containing Fe_{Re} or Re_{Fe} antisites, Fe1-Re1 or Fe1-Re4 interchanges, or V_{Sr} vacancy defects. However, the six (eight) nearest oxygen neighbors of the vacancy move away from (close to) V_{Fe} or V_{Re} (V_{O}) vacancies. The half-metallic (HM) character is maintained for the imperfect Sr_{2}FeReO_{6} containing Fe_{Re} or Re_{Fe} antisites, Fe1-Re4 interchange, V_{Fe}, V_{O} or V_{Sr} vacancies, while it vanishes when the Fe1-Re1 interchange or V_{Re} vacancy is presented. So the Fe1-Re1 interchange and the V_{Re} vacancy defects should be avoided to preserve the HM character of Sr_{2}FeReO_{6} and thus usage in spintronic devices. In the Fe_{Re} or Re_{Fe} antisites, Fe1-Re1 or Fe1-Re4 interchanges cases, the spin moments of the Fe (Re) cations situated on Re (Fe) antisites are in an antiferromagnetic coupling with those of the Fe(Re) cations on the regular sites. In the V_{Fe}, V_{Re}, V_{O}, or V_{Sr} vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice, while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μ_{tot} ( μ_{B}/f.u.) of the imperfect Sr_{2}FeReO_{6} containing eight different defects decrease in the sequence of V_{Sr} vacancy (3.50), V_{Re} vacancy (3.43), Fe_{Re} antisite (2.74), V_{O} vacancy (2.64), V_{Fe} vacancy (2.51), Re_{Fe} antisite (2.29), Fe1-Re4 interchange (1.96), Fe1-Re1 interchange (1.87), and the mechanisms of the saturation magnetization reduction have been analyzed.

The obvious circular dichroism (CD) and optical activity can be obtained based on the chiral metamaterial due to the plasmon-enhanced effect, which is very attractive for future compact devices with enhanced capabilities of light manipulation. In this paper, we propose a dual-chiral metamaterial composed of bilayer asymmetric split ring resonators (ASRR) that are in mirror-symmetry shape. It is demonstrated that the CD can get enhancement in the terahertz regime. Moreover, the CD can be further improved by modulating the asymmetry of ASRR. The enhanced CD effect in the terahertz regime has great potential applications in sensing, biomedical imaging, and molecular recognition.

Atomic-layer MoS_{2} ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy (AFM), x-ray diffraction (XRD), high-resolution transition electron microscopy (HRTEM), photoluminescence (PL), and x-ray photoelectron spectroscopy (XPS) characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation (002). The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasi-honeycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS_{2} under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS_{2}. The stoichiometric mole ratio of S/Mo is about 2.0-2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS_{2} under our experimental conditions.

Rare earth europium (Eu^{3+})-doped lithium tetraborate (Eu:Li_{2}B_{4}O_{7}) crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique (μT-Cz) for the first time. The grown crystals are subjected to powder x-ray diffraction (PXRD) analysis which reveals the tetragonal crystal structure of the crystals. UV-vis-NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO_{3} and BO_{4} bonding structure and the molecular associations are analyzed by Fourier transform infrared (FTIR) spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate (LTB) single crystal reveal that the observations of peaks at 258, 297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra. The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931 (Commission International d'Eclairage) color chromaticity diagram.

H_{2}O-based and O_{3}-based La_{x}Al_{y}O nanolaminate films were deposited on Si substrates by atomic layer deposition (ALD). Structures and performances of the films were changed by different barrier layers. The effects of different structures on the electrical characteristics and physical properties of the La_{x}Al_{y}O films were studied. Chemical bonds in the La_{x}Al_{y}O films grown with different structures and different oxidants were also investigated with x-ray photoelectron spectroscopy (XPS). The preliminary testing results indicate that the La_{x}Al_{y}O films with different structures and different oxidants show different characteristics, including dielectric constant, equivalent oxide thickness (EOT), electrical properties, and stability.

Metal Ti and its alloys have been widely utilized in the fields of aviation, medical science, and micro-electro-mechanical systems, for its excellent specific strength, resistance to corrosion, and biological compatibility. As the application of Ti moves to the micro or nano scale, however, traditional methods of planarization have shown their short slabs. Thus, we introduce the method of chemical mechanical polishing (CMP) to provide a new way for the nano-scale planarization method of Ti alloys. We obtain a mirror-like surface, whose flatness is of nano-scale, via the CMP method. We test the basic mechanical behavior of Ti-6Al-4V (Ti64) in the CMP process, and optimize the composition of CMP slurry. Furthermore, the possible reactions that may take place in the CMP process have been studied by electrochemical methods combined with x-ray photoelectron spectroscopy (XPS). An equivalent circuit has been built to interpret the dynamic of oxidation. Finally, a model has been established to explain the synergy of chemical and mechanical effects in the CMP of Ti-6Al-4V.

Design and characterization of a G-band (140-220 GHz) terahertz monolithic integrated circuit (TMIC) amplifier in eight-stage common-emitter topology are performed based on the 0.5-μm InGaAs/InP double heterojunction bipolar transistor (DHBT). An inverted microstrip line is implemented to avoid a parasitic mode between the ground plane and the InP substrate. The on-wafer measurement results show that peak gains are 20 dB at 140 GHz and more than 15-dB gain at 140-190 GHz respectively. The saturation output powers are -2.688 dBm at 210 GHz and -2.88 dBm at 220 GHz, respectively. It is the first report on an amplifier operating at the G-band based on 0.5-μm InP DHBT technology. Compared with the hybrid integrated circuit of vacuum electronic devices, the monolithic integrated circuit has the advantage of reliability and consistency. This TMIC demonstrates the feasibility of the 0.5-μm InGaAs/InP DHBT amplifier in G-band frequencies applications.

The dipole-dipole interaction model is employed to investigate the angular dependence of the levitation and lateral forces acting on a small magnet in an anti-symmetric magnet/superconducting sphere system. Breaking the symmetry of the system enables us to study the lateral force which is important in the stability of the magnet above a superconducting sphere in the Meissner state. Under the assumption that the lateral displacement of the magnet is small compared to the physical dimensions of our proposed system, analytical expressions are obtained for the levitation and lateral forces as a function of the geometrical parameters of the superconductor as well as the height, the lateral displacement, and the orientation of the magnetic moment of the magnet. The dependence of the levitation force on the height of the levitating magnet is similar to that in the symmetric magnet/superconducting sphere system within the range of proposed lateral displacements. It is found that the levitation force is linearly dependent on the lateral displacement whereas the lateral force is independent of this displacement. A sinusoidal variation of both forces as a function of the polar and azimuthal angles specifying the orientation of the magnetic moment is observed. The relationship between the stability and the orientation of the magnetic moment is discussed for different orientations.

One of the primary origins of the energy relaxation in superconducting qubits is the quasiparticle loss. The quasiparticles can be excited remarkably by infrared radiation. In order to minimize the density of quasiparticle and increase the qubit relaxation time, we design and fabricate the infrared filter and shield for superconducting qubits. In comparison with previous filters and shields, a nonmagnetic dielectric is used as the infrared absorbing material, greatly suppressing the background magnetic fluctuations. The filters can be made to impedance-match with other microwave devices. Using the as-fabricated infrared filter and shield, we increased the relaxation time of a transmon qubit from 519 ns to 1125 ns.

Recently, it has been demonstrated that memristors can be utilized as logic operations and memory elements. In this paper, we present a novel circuit design for complementary resistive switch (CRS)-based stateful logic operations. The proposed circuit can automatically write the destructive CRS cells back to the original states. In addition, the circuit can be used in massive passive crossbar arrays which can reduce sneak path current greatly. Moreover, the steps for CRS logic operations using our proposed circuit are reduced compared with previous circuit designs. We validate the effectiveness of our scheme through Hspice simulations on the logic circuits.

Waveguide-integrated Ge/Si heterostructure avalanche photodetectors (APDs) were designed and fabricated using a CMOS-compatible process on 8-inch SOI substrate. The structure of the APD was designed as separate-absorption-charge-multiplication (SACM) using germanium and silicon as absorption region and multiplication region, respectively. The breakdown voltage (V_{b}) of such a device is 19 V at reverse bias and dark current appears to be 0.71 μA at 90% of the V_{b}. The device with a 10-μ length and 7-μ width of Ge layer shows a maximum 3-dB bandwidth of 17.8 GHz at the wavelength of 1550 nm. For the device with a 30-μ-length Ge region, gain-bandwidth product achieves 325 GHz.

In the present study, graphene photonic crystals are employed to enhance the light extraction efficiency (LEE) of two-color, red and blue, light-emitting diode (LED). The transmission characteristics of one-dimensional (1D) Fibonacci graphene photonic crystal LED (FGPC-LED) are investigated by using the transfer matrix method and the scaling study is presented. We analyzed the influence of period, thickness, and permittivity in the structure to enhance the LEE. The transmission spectrum of 1D FGPC has been optimized in detail. In addition, the effects of the angle of incidence and the state of polarization are investigated. As the main result, we found the optimum values of relevant parameters to enhance the extraction of red and blue light from an LED as well as provide perfect omnidirectional and high peak transmission filters for the TE and TM modes.

The comparison of networks with different orders strongly depends on the stability analysis of graph features in evolving systems. In this paper, we rigorously investigate the stability of the weighted spectral distribution (i.e., a spectral graph feature) as the network order increases. First, we use deterministic scale-free networks generated by a pseudo tree-like model to derive the precise formula of the spectral feature, and then analyze the stability of the spectral feature based on the precise formula. Except for the scale-free feature, the pseudo tree-like model exhibits the hierarchical and small-world structures of complex networks. The stability analysis is useful for the classification of networks with different orders and the similarity analysis of networks that may belong to the same evolving system.

This paper investigates the consensus tracking problems of second-order multi-agent systems with a virtual leader via event-triggered control. A novel distributed event-triggered transmission scheme is proposed, which is intermittently examined at constant sampling instants. Only partial neighbor information and local measurements are required for event detection. Then the corresponding event-triggered consensus tracking protocol is presented to guarantee second-order multi-agent systems to achieve consensus tracking. Numerical simulations are given to illustrate the effectiveness of the proposed strategy.

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