Search

The magnetization behavior of the layered anisotropic high-Tc superconductor in the mixed state Hc1 H Hc2 has a feature that when the angle between the applied magnetic field H and the CuO plane (a-b plane) is less than a critical value ( L), the vortex lattice is converted from three-dimensional structure into two-dimensional structure, forming a phenomenon so called the lock-in transition, where the flux lines are completely parallel to the a-b plane, and the vertical component of the magnetic induction B丄 (perpendicular to the a-b plane) is consequently zero. So far, there have still existed the differences in the physical explanation of the lock-in phenomenon. For the lock-in phenomenon occurring in the region between the CuO planes, it can be considered to be caused by the transverse Meissner effect. However, for the one occurring in other extended correlated defect areas, such as twin boundaries in YBa2Cu3O7- (YBCO) crystal, this phenomenon is believed to be the results of the energy linearization of the vortices trapped in the defect channels. Many theoretical and experimental studies have revealed the existence of the lock-in behaviors related to the microstructure properties of the superconductor crystals. Therefore, the research of the lock-in transition behavior will be helpful to understand the intrinsic pinning properties of the layered anisotropic superconductors, and the phase transition process in the vortex system. In this paper, we systematically measure the magnetic torque signal in melt texture growth YBCO (MTG-YBCO) bulk and observe an abnormal lock-in transition behavior in the vortex system. The critical angle of the lock-in transition is found to be directly proportional to the strength of the magnetic field, which is contrary to the observations in the common cases. According to the framework of the Ginzburg-Landau theory and the kink structure model of the vortex line, we discuss the abnormal phenomenon, and propose that there is a type of extend-correlated defect structure, which is parallel to the a-b plane, in the MTG-YBCO crystal. The relationship between the critical angle of the lock-in transition to the temperature and the magnetic field is established theoretically, and the theoretical results coincide well with the torque measurements.

Since its discovery in 2004, the graphene has attracted great attention because of its unique chemical bonding structure, which has excellent chemical, thermal, mechanical, electrical and optical properties. Due to the graphene being a zero band gap material, it has a limited development in the field of nano electronics. Therefore, in order to broaden its application scope, it is very important to carry out a study on opening the band gap of graphene. In this paper, we construct three models, i.e., the intrinsic graphene model, the N-doped graphene model, and the B-doped graphene model. We study the energy band structures and the electronic densities of states for the intrinsic graphene and the N/B doped graphenes with different doping concentrations. Furthermore, we study their optical and electronic properties including the absorption spectra, the reflection spectra, the refractive indexes, the conductivities, and the dielectric functions. The results are as follows. 1) The electronic states in the vicinity of the Fermi level for the intrinsic graphene are mainly generated by the C-2p orbits, while the electronic states in the vicinity of the Fermi level for the N/B doped graphenes are mainly generated through the hybridization between C-2p and N-2p/B-2p orbits. N doped graphene is of n-type doping, while B doped graphene is of p-type doping. 2) Compared with that of the intrinsic graphene, the Fermi level of N doped graphene moves up 5 eV. In the meantime, the band gap is opened, and the Dirac cone disappears. On the contrary, the Fermi level of B doped graphene moves down 3 eV compared with that of the intrinsic graphene. However, like the N doping, the band gap is also opened, and the Dirac cone disappears. Furthermore, the N doping is more effective than the B doping in opening the energy gap of the graphene for the same N/B doping concentration. 3) The N/B doping can cause the optical and electronic properties of the graphene to change, and exert great influences on the absorption spectrum, reflection spectrum, the refractive index, and the dielectric function, however it has little influence on the conductivity. When the energy of the incident wave is larger than a certain value, the optical and electrical properties of the intrinsic graphene remain unchanged. Besides, for the above case, the corresponding energies for the N/B doped graphenes are smaller than that for the intrinsic graphene. In addition, the energy for the B doped graphene is smallest. The conclusions of this paper can provide a theoretical basis for the application of graphene in optoelectronic devices.

In this article, we take partially coherent electromagnetic Gaussian-Schell model (EGSM) beam as a research object. Based on the unified theory of coherence and polarization and the generalized Stokes parameters of random electromagnetic beams, the expressions of degree of polarization (DoP) and orientation angle of EGSM beam that propagates in the slant atmospheric turbulence, are derived. And the expressions are used to investigate the difference in polarization property of EGSM beam between propagating along an uplink path and a downlink path in the atmospheric turbulence. The results show that under the same conditions, the DoP distribution of EGSM beam propagating along a downlink path is more concentrated than that along an uplink path. When EGSM beam propagates along a downlink path, the maximum DoP corresponding to the propagation distance is larger than along an uplink. Therefore, when EGSM beam propagates along a downlink path, the detector can receive beam information at the longer distances.

Atmospheric turbulence can cause random variations of the refractive index, resulting in a spatial inhomogeneity. When a Laguerre-Gaussian beam is propagating through the atmospheric turbulence, spatial inhomogeneity can bring about the change of photon wave function that causes variations in the orbital angular momentum. This article discusses how turbulence media change the orbital angular momentum of photons as to form different photon states, when the Laguerre-Gaussian beam is propagating in a slant-path atmospheric turbulence, by calculating the weight of the spiral harmonic component of the beam energy. Analysis of the variations of orbital angular momentum of Laguerre-Gaussian beam in the turbulent medium has been carried out.

In this paper, we describe orbital angular momentum entangled photon pair entanglement in atmospheric channel. The Von Karman spectrum of turbulence is used to create a model of two-photon pair entanglement. The effects of atmospheric turbulence on the entanglement of entangled photon pairs of different orbital angular momentum bases are analyzed. The obtained results are as follows because of the presence of atmospheric turbulence, the entanglement of entangled photon pairs decreases with the increase of the propagation distance z in the atmosphere channel. The entanglement of the entangled photon pairs decreases with the increase of transmission distance. The bigger the turbulence intensity, the faster the entanglement decline and the shorter the propagation distanceis. In the same intensity of atmospheric turbulence of the atmospheric channel, the bigger the orbital angular momentum index, the slower the entanglement decline and the further the propagation distanceis.

The estimation of pulsar period is important for pulsar searching, observation and timing. In this paper, the frequency-domain method which is popular in periodicity searches is analyzed, and further more, a novel method in time-domain is proposed to estimate the cyclo-period of pulsars based on the second-order cyclo-stationary model of the radiation signal. Firstly, the discrete-time observing signal is blocked by assumed period which is alterable. Then, the correlation estimations and their sample variances are computed each as a function of blocking operator index, where the largest peaks display a periodic pattern, from which the cyclo-period can be obtained. Using this method, the period of PSR J0437-4715 with single pulse is estimated well based on original signal, and the period of PSR B1821-24 with double pulses is also estimated based on the simulated signal. The same work is done for the observed data from ATNF EPN pulsar database. The simulation results and the experimental results for many pulsars show that compared with the classical Fourier-transform method, this algorithm is non-sensitive to the noise, and it is effective even though in the case of low signal-to-noise ratio. And it is of low computation complexity compared with the bispectrum coherence method. This method possesses higher popularization value in real-time observation and processing for weak pulsar signal, though it does not work well in dealing with noncontinuous observing data.

In this paper, the Monte Carlo method is employed to simulate the ultraviolet light scattering transmission. The three modes of ultraviolet (UV) no-line-of-sight (NLOS) communication are analyzed. The UV NLOS transmission model based on the Monte Carlo method is proposed. The path losses of single and multiple scatterings and the coverage area of three UV NLOS modes are simulated by using the Monte Carlo method. Finally, we obtain the conclusion that multiple scattering and single scattering basically have the same path loss. The coverage of NLOS (a) is smallest, but omni-direction is good. The coverage of NLOS (b) is larger, but it is directional. The coverage of NLOS (c) is largest, but it is strongly directional.

We describe the high order elliptic hermite gaussian beam and the average orbital angular momentum of single-photon, and analyze some situations of the change of orbital angular momentum, briefly by the simulation. Finally, the probability distribution and changes in the probability distribution within the range of space for the single-photon orbital angular momentum are analyzed. The results show that the change magnitude of the single-photons average orbital angular momentum varies with the material when the high order elliptic Hermite-Gaussian beam interacts with mater.

The propagation properties and scattering characteristic of a beam with orbital angular momentum transmission were researched by using the generalized Lorenz-Mie theory. Based on the research on the scattering of the Gaussian beam from single sphere，the intensity distributions of LGB beam at different propagation distance is analyzed. Without considering the relation between scattering and phase shift，the beam coefficients is obtained by the solution of scattering cross section，and the LGB is expanded in terms of the vector spherical harmonics as fundamental Gaussian beam. The scattering of the beam with orbital angular momentum from single sphere located on the propagation axis is studied. The influence of scattering intensity and angular distribution on scattering characteristic for different beam width is discussed by numerical simulation，and compared with those for the plane wave. The results show that when the beam waist radius is very small，the beam waist radius has serious influence on the decay rate. When the beam waist radius is relatively large，the influence is similar to that of plane wave.

Supersonic radiation transport, where the ratio of the radiation wave front velocity to the material sound speed was more than 10, has been investigated experimentally in the low-density foam. Four beams of 0.35μm laser with pulse d uration of 1ns and 2kJ of total energy entered into a hohlraum to create intense x-ray radiation that heated C66H12

A high Z cylindrical hohlraum was used to produce xray radiation flux, whic h was used to drive shock waves in an Al step sample. The radiation temperature i s 15 5eV. Experiments were carried ont on `Shenguang II' laser facility, with eight 2 50J, 0.35μm wavelength, 1ns Gaussian laser pulses. The planar and preheatfre e s ho ck wave was generated and a clear image of shock and preheat wave was obtained . The shock wave velocity and pressure was 31.2km/s and 17.5×1011Pa, respectively.The radiation temperature measured by streaked pyrometer, was consistent with th at measured with a soft x-ray spectrometer which views through the laser entran ce hole.

On the basis of the two-dimensional (2D) characteristics of the superconducting transportation as well as Josephson weak link behaviors in granular YBCO films,a 2D Josephson junction array is proposed as a model system for this film.Using this simplified model,we have discussed the decoupling procedure of vortex-antivortex pairs by bias current,and analytically developed temperature distribution of free vortices n(T,I) below TKT.As compared with experimental results,we find that the temperature dependency of n(T,I) is similar to the behaviors of microwave response of granular YBCO films near K-T transition temperature.This similarity implies,to a certain extent,some intrinsic relationship between vortex-antivortex decoupling and non-equilibrium radiation response dissipation in the high-Tc superconducting granular films.

We study the pairing symmetry in high-temperature superconductors from the point of view of group theory analysis in the framework of Ginzburg-Landau model. By considering an orthorhombic distortion from C4v point group because of the correlation of intralayers, the two apparent transitions needed in earlier work on mixed s and d state have been removed. The structure of a single vortex is presented by solving the Ginzburg-Landau wave function equations of the mixed s±idx2-y2 state. The analysis of the magnetic field dependence of the transport behaviors including the critical current and the R-T curve expansion reveals the origin of the so-called “eigen-pinning effect” and offers a good interpretation of the experimental observations.

The characteristic of microwave radiation (λ＝8mm) response of YBCO granular films was reported. Experimental results show that the response behavior can be described with nonequilibrium response effect, instead of thermal effect model. Near below the transition temperature T∞, nonequilibrium microwave response signal decays gradually and disappears with the sample resistance becoming zero. It was also found that the response signal is very sensitive to a weak magnetic field. The sample I-V curve was studied carefully, and the Kosterlitz-Thouless transition model can be used to describe the two-dimensional transport characteristic of the YBCO granular films. Based on the analysis and experimental results, we believe that the mechanism of nonequilibrium microwave response may be related with the breaking of the votex-antivotex pair in high Tc superconductor.

We present descriptions of the pairing symmetry in high-temperature superconductors.Analysis of the Josephson tunneling experiments based on the asymptotic s±id state has, to some extend,demonstrated the validity of the model,and the comparison of the theoretical calculations with the dichromatic observations in this kind of material has been in favor of the Γ1+Γ4 representation argument.The possible appearance of the fractional quantum flux vortex related to the specific mixed pairing symmetry has also been discussed.

The structure of a single vortex in a superconductor with s+id symmetry is given employing a recently developed Ginzburg-Landau theory by the method of relaxation iteration.We also studied the variation of respective components s and d with the temperature and magnetic field.Finally,we give the curve of the upper critical field along with transition temperature in mixed wave consideration.Our result is in qualitative agreement with the experiment data.

Atomic clock is an extremely precise oscillator,but the increase of precision of it is limited by the noise in it.The period and chaos in an atomic clock is simulated by using a type of Duffing equation.Statistical characteristis of various chaos are discussed.According to the Lyapunov exponent of the atomic clock signal,the chaos in the clock and its motivational mechanism is analyzed.Measured data from CSAO Laboratory during 1994.6.1—8.20 are processed and statistical characteristics of chaos described.

Experiments showed that the non equiliubrium optical response of epitaxial YBa_ 2Cu _3O7-δ films below T c existed with the illumination of He Ne laser (λ=063μm). We have also found that near the transition region, where dR/dT is vanishing, the optical response becomes a strong nonlinear functions of current. A model was presented to explain the mechanism of the nonlinear behavior based on the interactions between photoexcited quasiparticles and the vortex in high T c superconductor. We believe that the mechanism of the dissipation induced by light illumination in transition region may be correlated with the mechanism of “irreversibility line” or that of “broaden resistive transition” in magnetic fields.

An analytical method is presented for investigating the resonant behaviors of composed resonator formed by deporviting the c caxis oriented ＹＢａ2Ｃｕ3Ｏ７－δ (δ≈≈0) thin film on ＬａＡｌＯ3（００１）. The concept of the negative dielectric medium for a superconductor is introduced within the framework of the two-fluid model, which permits us to treat a superconductor as any other penetrable materials so as only its electromagnetic property is concerned. A conformal transformation is further suggested to map the original open boundary value problem to a closed one. This not only makes the original problem readily solved by using the variational technique, but also is powerful for the analyzing a kind of problems such as the propagation characteristics of the superconducting microstripe and coplannar waveguiding structures.

Radiation temperature in hohlraums is diagnosed using two soft X-ray spectrometers and multi-pinhole soft X-ray streak camera. We have improved the accuracy taking plasma closure effects of the diagnostic hole into consideration. We have obtained 2D-images and processes of the hole closure and radiation temperature in the hohlraums νs time. A preliminary model of the closure effect of diagnostic hole is proposed based on the experimental data.