Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Electrically insulating properties of the 5d double perovskite Sr2YOsO6
No full textWorld Premier International Research Center Initiative (WPI Initiative, MEXT, Japan); Japan Society for the Promotion of Science (JSPS) [15K14133, 16H04501]; Bilateral Open Partnership Joint Research Projects; Natural Science Foundation of Shanghai [17ZR1443300]; Project of Science and Technology of Guangdong Province [2013A011402006]A high-pressure-synthesized double perovskite Sr2YOsO6 was investigated by synchrotron X-ray diffraction and measurements of its magnetic susceptibility, specific heat capacity, complex impedance, and complex dielectric constant. It crystallized into a monoclinic double perovskite structure (P2(1)/n) with complete ordering of the Y and Os atoms. Its magnetic behaviors, including the antiferromagnetic transition temperature (similar to 52 K), Curie-Weiss effective moment [3.48(5) mu B/Os], and Weiss temperature [- 350.1(7) K], were close to the respective values of Sr2YOsO6 previously synthesized without an applied pressure of 6 GPa. Transport property measurements revealed that the lower limit of the activation energy was 192(1) meV and the charge gap remained open regardless of the presence of magnetic order, conflicting with the electron delocalization predicted by theoretical calculations. Further consideration, including theoretical and experimental investigations of the roles of spin-orbit coupling and U of the 5d electrons of Os 5d-t(2)g(3), may assist in understanding the general magnetic and insulating behaviors of quasi-half-filled 5d-t(2)g(3) oxides in the perovskite category toward the use of 5d double perovskite for magnetic applications. Published by AIP Publishing
Enhancement of proton acceleration by a right-handed circularly polarized laser interaction with a cone target exposed to a longitudinal magnetic field
No full textNational Key Research and Development Program of China [2016YFA0401101]; National Natural Science Foundation of China [11475030, 11375032, 11575035, 11435011]Our previous research [J. X. Gong et al. Phys. Plasmas 24, 033103 (2017)] shows that in the presence of an external longitudinal magnetic field, there is no cut-off density when a right-handed (RH-) circularly polarized (CP) laser propagates in the plasmas. In this work, the proton acceleration driven by an RH-CP laser interaction with a pre-magnetized cone target filled with a preformed plasma is investigated under the mechanism of target normal sheath acceleration. The strength of the external magnetic field considered in this paper is comparable to that of the incident laser. The two-dimensional particle-in-cell simulation results show that with an external longitudinal magnetic field, both the energy and yield of protons accelerated by the sheath electric field at the rear of the target are remarkably increased because of the higher coupling efficiency from RH-CP laser energy to electrons and the more efficient electron acceleration. Electrons can be converged remarkably by the external magnetic field and the divergence of protons can be controlled evidently by the collimated electrons. The maximum cut-off energy of protons with an imposed longitudinal magnetic field can be promoted to be as high as 82MeV. Detailed simulation results show that the maximum energy of protons increases with the increasing initial external magnetic field. Published by AIP Publishing
Nanosecond double-pulse fiber laser with arbitrary sub-pulse combined based on a spectral beam combining system
No full textNational High Technology Research and Development Program of China [2014AA041901]; NSAF Foundation of National Natural Science Foundation of China [U1330134]; National Natural Science Foundation of China [61308024]In order to improve the processing efficiency and quality of nanosecond pulse laser drilling, a new double-pulse technique is put forward. Two single pulse lasers with different pulse duration or different repetition rate are spectrally combined by a home-made polarization-independent multilayer dielectric reflective diffraction grating. The pulse energy of single lasers and the inter-pulse separation can both be set at one's option. Then, double-pulse lasers represent two closely conjoint pulses with tunable pulse duration and tunable repetition rate and tunable pulse energy and tunable inter-pulse separation are obtained
Identifying the source of super-high energetic electrons in the presence of pre-plasma in laser-matter interaction at relativistic intensities
No full textNational Natural Science Foundation of China [11304331, 11174303, 61221064]; National Basic Research Program of China [2013CBA01504, 2011CB808104]; USDOE at UCSD [DENA0001858]The generation of super-high energetic electrons influenced by pre-plasma in relativistic intensity laser-matter interaction is studied in a one-dimensional slab approximation with particle-in-cell simulations. Different pre-plasma scale lengths and laser intensities are considered, showing an increase in both particle number and cut-off kinetic energy of electrons with the increase of pre-plasma scale length and laser intensity, the cut-off kinetic energy greatly exceeding the corresponding laser ponderomotive energy. A two-stage electron acceleration model is proposed to explain the underlying physics. The first stage is attributed to the synergetic acceleration by longitudinal electric field and counter-propagating laser pulses, and a scaling law is obtained with efficiency depending on the pre-plasma scale length and laser intensity. These electrons pre-accelerated in the first stage could build up an intense electrostatic potential barrier with maximal value several times as large as the initial electron kinetic energy. Some of the energetic electrons could be further accelerated by reflection off the electrostatic potential barrier, with their finial kinetic energies significantly higher than the values pre-accelerated in the first stage
First-principles quantum transport method for disordered nanoelectronics: Disorder-averaged transmission, shot noise, and device-to-device variability
No full textShanghaiTech University start-up fund; The Thousand Young Talents Plan; Shanghai "Shuguang Plan"; National Basic Research Program of China [2012CB921304]; NNSF-China [61376105, 21421003]Because disorders are inevitable in realistic nanodevices, the capability to quantitatively simulate the disorder effects on electron transport is indispensable for quantum transport theory. Here, we report a unified and effective first-principles quantum transport method for analyzing effects of chemical or substitutional disorder on transport properties of nanoelectronics, including averaged transmission coefficient, shot noise, and disorder-induced device-to-device variability. All our theoretical formulations and numerical implementations are worked out within the framework of the tight-binding linear muffin tin orbital method. In this method, we carry out the electronic structure calculation with the density functional theory, treat the nonequilibrium statistics by the nonequilbrium Green's function method, and include the effects of multiple impurity scattering with the generalized nonequilibrium vertex correction (NVC) method in coherent potential approximation (CPA). The generalized NVC equations are solved from first principles to obtain various disorder-averaged two-Green's-function correlators. This method provides a unified way to obtain different disorder-averaged transport properties of disordered nanoelectronics from first principles. To test our implementation, we apply the method to investigate the shot noise in the disordered copper conductor, and find all our results for different disorder concentrations approach a universal Fano factor 1/3. As the second test, we calculate the device-to-device variability in the spin-dependent transport through the disordered Cu/Co interface and find the conductance fluctuation is very large in the minority spin channel and negligible in the majority spin channel. Our results agree well with experimental measurements and other theories. In both applications, we show the generalized nonequilibrium vertex corrections play a determinant role in electron transport simulation. Our results demonstrate the effectiveness of the first-principles generalized CPA-NVC for atomistic analysis of disordered nanoelectronics, extending the capability of quantum transport simulation
Origin of arbitrary patterns by direct laser writing in a telluride thin film
No full textNational Natural Science Foundation of China [51172253, 61137002]A crystalline telluride (Te) thin film was prepared by a radio frequency magnetron controlling sputtering method. The fabrication of arbitrary patterns was achieved successfully by our home-built direct laser writing system in the prepared Te thin film. To elucidate the mechanism of pattern formation, micro Xray diffraction, micro Raman spectra and micro reflective spectra before and after exposure were analyzed in detail. The results reveal that the occurrence of arbitrary patterns may be ascribed to the decreased grain size in the Te thin film, which can further be confirmed by the results of AFM and section images of the Te thin film. It is a simple and cost-effective method for arbitrary pattern fabrication based on the reduction of grain size in the laser writing process
Origin of the plasma scalds in dielectric coatings induced by 1 omega laser
No full textChinese National Natural Science Foundation [61308021]; International Science and Technology Cooperation Program of China [2012DFG51590]The plasma scalds initiated by a 1053 nm (1 omega) nanosecond laser are separated from the defect-induced damage pits, which is verified as a result of the ionization wavefront with the subnanosecond laser. Considering the beam reflection from solid-state absorption fronts during the damage process, a theoretical scalding threshold about 6: 84 J/cm(2) (12ns) based on the energy required to start an air avalanche is evaluated and agrees well with the experimental scalding threshold. The occurrence order of the initial explosion and subsequent ionization wavefront is verified to explain most of the damage morphologies caused by the 1 omega laser. In addition to the significance in laser conditioning or cleaning for a high-power laser system, the results also indicate that through the occurrence of plasma scalds it is possible to mark the onset time of air plasma during laser-coating interaction. (C) 2016 AIP Publishing LLC
Reversible Phase Change Characteristics of Cr-Doped Sb2Te3 Films with Different Initial States Induced by Femtosecond Pulses
No full textStrategic Priority Research Program of the Chinese Academy of Sciences [XDA09020402]; National Integrate Circuit Research Program of China [2009ZX02023-003]; National Natural Science Foundation of China [61261160500, 61376006, 61401444, 61504157]; ScienceAs a kind of chalcogenide alloy, phase change material has been widely used as novel storage medium in optical disk or electrical memory: In this paper, femtosecond pulses are used to study the, reversible phase transition processes of Cr-doped Sb2Te3 films with different initial states. The SET processes are all induced by multiple pulses and relate to the increase of crystallized partial in the irradiated spot. When the Cr. concentration is 5.3 at % or 10.5 at %, the crystallization mechanism is still growth-dominated as Sb2Te3, which is beneficial for high speed and high density storage, whereas the necessary crystallization energy increases with more Cr-dopants, leading to higher amorphous thermal stability. RESET results by multiple pulses-Show that Cr-dopants will not increase the power consumption, and the increase in Cr-dopants could greatly increase the antioxidant capacity. Single-pulse experiments show that the RESET process involves the competition of melting/amorphization and recrystallization. The reversible SET/RESET results on different initial states are quite different from each other, which is mainly due, to the different surroundings around the irradiated spot. Crystalline surroundings provide higher thermal conductivity and lead to easier crystallization, whereas amorphous surroundings were the reverse. All in all, Cr-doped Sb2Te3 films with suitable composition have advantages for storage with high density, better thermal stability, and lower power consumption; and the suitable initial states could ensure better reversible phase transition performances
Size-dependent saturable absorption and mode-locking of dispersed black phosphorus nanosheets
No full textNational Natural Science Foundation of China (NSFC) [61308034, 61522510, 51302285, 61505105, 61675217]; External Cooperation Program of BIC, CAS [181231KYSB20130007]; Shanghai Yangfan Program [14YF1401600]; State Key Lab Project of Shanghai Jiao Tong UnivSize dependence of the saturable absorption (SA) property for black phosphorus (BP) was investigated. Three types of BP dispersions with different sizes were prepared using the liquid phase exfoliation method. By fitting the Z-scan data with the analytical solution of the propagation equation, the SA coefficients alpha(NL) and the imaginary part of the third order optical susceptibility Im chi((3)) are compared at two specific wavelengths, one above the bandgap of the BP monolayer at 515 nm and another between the bandgaps of the monolayer and bulk at 1030 nm. A figure of merit (FOM, vertical bar Im chi((3))/alpha(0)vertical bar, alpha(0) linear absorption) was employed to assess the SA performance of the three different dispersions. The FOM, about (2.1 +/- 0.3) x 10(-14) esu cm at 515 nm, hardly depends on the size and hence the layer number of the dispersed BP nanosheets, whereas that at 1030 nm decreases from (1.14 +/- 0.20) x 10(-14) to (0.50 +/- 0.02) x 10(-14) esu cm when the size of the nanosheets becomes smaller. (C) 2016 Optical Society of Americ