bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and functions of graphene–molecule–graphene single-molecule junctions
Authors: Yang Caiyao , Qin Anjun , Tang Ben Zhong , Guo Xuefeng
Published: March 2020

The past two decades have witnessed increasingly rapid advances in the field of single-molecule electronics, which are expected to overcome the limitation of the miniaturization of silicon-based microdevices, thus promoting the development of device manufacturing technologies and characterization means. In addition to this, they can enable us to investigate the intrinsic properties of materials at the atomic- or molecular-length scale and probe new phenomena that are inaccessible in ensemble experiments. In this perspective, we start from a brief introduction on the manufacturing method of graphene–molecule–graphene single-molecule junctions (GMG-SMJs). Then, we make a description on the remarkable functions of GMG-SMJs, especially on the investigation of single-molecule charge transport and dynamics. Finally, we conclude by discussing the main challenges and future research directions of molecular electronics.
Investigation of near-stoichiometric polycrystalline CuInSe2 thin films by photoreflectance spectroscopy
Authors: Levcenko S. , Stange H. , Choubrac L. , Greiner D. , Heinemann M. D. , Mainz R. , Unold T.
Published: March 2020

The bandgap of CuInSe2 thin film photovoltaic absorbers depends on the Cu content, although the nature of this dependence is still a matter of debate. While theoretical results predicted a widening or stable bandgap with decreasing Cu content, the few experimental data available point to a narrowing of the bandgap. Here, we apply photoreflectance spectroscopy at room temperature to near-stoichiometric polycrystalline CuInSe2/CdS heterojunctions with a lateral Cu gradient to analyze the electronic transitions in the vicinity of the fundamental absorption edge of CuInSe2 absorber as a function of Cu deficiency. The results indicate that the lowest bandgap transition at 1.02 eV notably decreases by 20–30 meV for slightly Cu deficient samples, strengthening the case for an association of a lower Cu content with a narrower bandgap. In contrast, the higher energy transition at 1.25 eV does not show a redshift, which requires further theoretical explanation.
Adlayer growth vs spontaneous (near-) surface alloy formation: Zn growth on Au(111)
Authors: Schüttler Konstantin M. , Bansmann Joachim , Engstfeld Albert K. , Behm R. Jürgen
Published: March 2020

As part of an extensive effort to explore the function of Au/ZnO catalysts in the synthesis of methanol from CO2 and H2, we have systematically investigated the temperature dependent growth, structure formation, and surface intermixing of Zn on the herringbone reconstructed Au(111) surface and the thermal stability of the resulting surfaces by scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS). After Zn deposition at low temperatures, at about 105 K (STM) or below (XPS), we observed nucleation and two-dimensional growth of Zn islands mainly at the elbow sites of the Au(111) herringbone reconstruction. This results in local perturbations of the reconstruction pattern of the Au(111) substrate, which can create additional nucleation sites. XPS data indicate that Zn dissolution into deeper layers is kinetically hindered under these conditions, while local exchange with the Au surface layer, in particular at the elbow sites during nucleation, cannot be excluded. Zn deposition at room temperature, in contrast, results in near-surface alloy formation with a strongly distorted pattern of the herringbone reconstruction and condensation of the Zn and exchanged Au adatoms at ascending steps, together with some loss of Zn into deeper layers. Upon annealing, Zn atoms diffuse to lower layers and eventually to the Au bulk, and the surface successively regains its original Au(111) herringbone structure, which is almost reached after 500 K annealing. Compared with previous reports on the growth of other metals on Au(111), Zn shows a rather high tendency for intermixing and near-surface alloy formation.
Photodissociation dynamics of OCS near 128 nm:
S(3PJ=2,1,0),
S(1D2) and S(1S0) channels
Authors: Wang Si-wen , Yuan Dao-fu , Chen Wen-tao , Tang Ling , Yu Sheng-rui , Yang Xue-ming , Wang Xing-an
Published: March 2020

Here we report the study of the photodissociation dynamics of carbonyl sulfide in the vacuum ultraviolet region using the time-sliced velocity map ion imaging technique. Images of S(3PJ=2,1,0), S(1D2) and S(1S0) products were measured at four photolysis wave-lengths of 129.32, 128.14, 126.99, and 126.08 nm, respectively. Four main dissociation channels: S(3PJ=2,1,0)+CO(X1Σ+), S(3PJ=2,1,0)+CO(A3Π), S(1D2)+CO(X1Σ+) and S(1S0)+CO(X1Σ+) channels, have been clearly observed and identified. Vibrational states of the CO co-products were partially resolved in the experimental images. From these images, the product total kinetic energy releases, the branching ratios and angular distributions of products have been derived. While the S(3PJ=2,1,0)+CO(A3Π) product channel is formed through the adiabatic dissociation process after the excitation to the (31Σ+) excited state, the results suggest that strong nonadiabatic coupling plays an important role in the formation of other three channels.
A new pressurization-insulation and pre-sealing system to improve pressure in cubic press from 6 GPa to 12 GPa
Authors: Wang Yipeng , Kou Zili , Zhang Jiawei , Chen Shijiang , Zhang Lu , Peng Bo , Zhao Mengxi , Jiang Mingli , Yin Xiaoshuang , He Duanwei
Published: March 2020

In this paper, a pressurization-insulation and pre-sealing (PIPS) system is designed to increase the cell pressure of the widely used large volume cubic press without sacrificing cell volume. The sample chamber was sandwiched between a pair of tungsten carbide anvils used as the pressurization system. Ultra-high pressure in the cavity was up to about 12 GPa, and the pressure limit had increased by 100% in contrast with that of an anvil-gasket (AG) system. Furthermore, the confining pressure around the sample chamber was supported by grade 304 stainless steel and a zirconia–calcium oxide solid solution before a press load of 2.8 MN was applied as well as by four surrounding anvils. The relationship between the sample chamber pressure and the press load for this system was calibrated at room temperature using transitions in zinc telluride. With samples of similar volumes, the proposed system retained not only stability but also uniform pressure and temperature fields, in contrast with the AG system and the anvil-preformed gasket cubic press pressurization system. The results of more than 20 experiments show that the proposed PIPS system can operate stably under a press load of 4.2 MN, corresponding cell pressure of 10 GPa, and temperature in the cell exceeding 1800 °C by using graphite as a heater.
Grazing pressure and tree competition affect cattle performance and native pastures in Eucalypt woodlands of Queensland, north-eastern Australia
Authors: Hall Trevor J. , Silcock Richard G. , Mayer David G.
Published: March 2020

Context
Well managed grazing pressure will optimise animal and pasture production, and preserve the soil to maintain a viable beef business on native pastures in eucalypt woodlands.

Aims
A cattle grazing experiment was established to measure animal and pasture performance under management practices used in the Aristida/Bothriochloa native pastures in central Queensland.

Methods
Performance of Brahman-cross steers and pastures were measured in an experiment with three grazing pressures by two tree densities in a Eucalyptus populnea woodland in north-eastern Australia over 8 years in paddocks of 4–18 ha.

Key results
At low grazing pressure with trees killed by herbicide (‘cleared’), stocking rate increased 35% as pasture composition and biomass improved over 8 years. At low grazing pressure where treed, stocking rate remained constant, however, at high grazing pressure where treed, it was reduced after 4 years. The annual liveweight gain increased from 0.37 to 0.45 to 0.51 kg/head.day as grazing pressure was reduced from high to medium to low grazing pressure respectively, and across grazing pressures it decreased from 0.49 where cleared to 0.39 kg/head.day where treed. Liveweight gain per hectare increased under low grazing pressure and declined at medium and high pressures. Body condition scores responded positively to lower grazing pressure and a lack of tree competition to pastures. This treatment combination also produced higher animal sale values. Pasture biomass, basal area and ground cover were all affected negatively by increasing grazing pressure.

Conclusions
Grazing 25% of autumn pasture improved dry matter production, species composition and land condition, and increased steer growth rates, body condition and their market value. This grazing pressure produced an increasing trend in stocking rates relative to the decline at higher grazing pressures. Higher liveweight gain/ha was produced initially at high grazing pressure (75% utilisation), however, after 4 years animal condition and pastures deteriorated, requiring a reduction in stocking rate to maintain the condition of both the remaining animals and the pastures. Managing tree competition to pastures is necessary to maintain the higher animal production potential.

Implications
This objective information demonstrates the benefits for cattle, pastures and long-term economic outcomes of managing for conservative grazing pressure and controlling tree competition to pasture in this woodland. Applying these findings can improve beef business outcomes and provide management groups with objective educational resources.
Genetic potential of Sindhi cattle for A2 milk production
Authors: Schettini Gustavo Pimenta , Lambert Sabrina Mota , da Silva Souza Bárbara Maria Paraná , Costa Raphael Bermal , de Camargo Gregório Miguel Ferreira
Published: March 2020

ContextCow milk is consumed in many countries. However, its consumption can be associated with gastrointestinal disorders in humans. The genetic profile of β-casein is one of the factors responsible for these disorders and the A1 variant is a causal agent. The β-casein A1 leads to the formation of bioactive peptides, which trigger intestinal reactions. The same is not observed for the A2 allele. A2 milk is obtained from cows with the A2A2 genotype. The identification of breeds and selection of animals for A2 milk production is important for public health and animal production. The Sindhi cattle (Bos taurus indicus) possesses characteristics such as adaptation to hot climate, resistance to parasites and utilisation of low-quality forage that are important for rearing in the tropics.
AimsThe objective of the present study was to genotype the single-nucleotide polymorphism (SNP) that forms A1 and A2 alleles of the β-casein in Sindhi cattle.
MethodsIn total, 348 Sindhi animals were used. DNA was extracted from hair follicles and submitted to PCR-sequencing for genotyping.
Key resultsAllele frequency for A2 was 0.94 and for A1 it was 0.06. Genotype frequencies were 0.90 (A2A2), 0.09 (A1A2) and 0.01 (A1A1). The frequency of the A2A2 genotype in Sindhi cattle was similar to or higher than those found in zebu breeds and higher than those reported for specialised taurine breeds.
ConclusionsThis high frequency of the A2A2 genotype indicates a genetic potential of the breed for A2 milk production and easy, assisted selection (if that is the intention).
ImplicationsThis information gives importance to the breed and permits to add value to dairy product derived from it. It may increase producer’s income through producing and marketing A2 milk.
Stock structure of dusky flathead (Platycephalus fuscus) to inform stocking management
Authors: Taylor Matthew D. , Becker Alistair , Quinn Jane , Lowry Michael B. , Fielder Stewart , Knibb Wayne
Published: March 2020

Delineating stocks and quantifying population structure are critical for the management of exploited populations, but the stock structure of many species remains unclear. In New South Wales (NSW), Australia, a marine stock enhancement program for dusky flathead (Platycephalus fuscus) is developing, and knowledge of stock structure is required to inform enhancement strategies, as well as to support broader fisheries management. A combination of mitochondrial and microsatellite markers was used in this study to evaluate structuring among fish from eight estuaries, spanning the majority of the NSW coast. Pairwise comparisons of mitochondrial haplotypes revealed that seven of the eight estuaries were genetically homogeneous (St Georges Basin was distinct). Moreover, analysis of molecular variance showed that 97% of sequence diversity occurred within estuaries. The results from microsatellite markers were almost identical to those for mitochondrial DNA, with St George’s Basin having the only distinct genotype, and within estuary variation accounting for 99% of the genotype variation. Isolation by distance analysis showed that <5% of genetic variation was due to distance. These results indicate that dusky flathead forms a single stock across NSW, where mixing most likely occurs during early life phases and through limited adult migration. The outlying estuary, St Georges Basin, likely suffers from limited connectivity due to a constricted entrance, and it is possible that stocking may improve local genetic diversity.
Thinking out of the box
Authors: van den Heerik Romy A. M. , Droog Ellen , Jong Tjien Fa Melanie , Burgers Christian
Published: March 2020

Metaphor production is a creative process of thinking out of the box, which can be of great communicative value to
language users. In this study, we explored how metaphor production can be stimulated by different types of cues in an internet
environment. Participants (N = 318) were invited to co-create a metaphorical campaign slogan in a social media
setting with randomly selected sets of real campaign slogans. We measured how linguistic (metaphor markers) and social media cues
(likes) prompt direct metaphor. Results show that the metaphor marker ‘so’ stimulated metaphor production. Likes for previously
posted metaphorical slogans did not affect the creation of a metaphor. We found a correlation between the actual and
self-perceived creativity of the co-created slogans. Besides, the co-created metaphors both echoed and deviated from previously
posted campaign slogans, leading to different degrees of creativity. Co-creation in a social media setting seems a fruitful
environment for metaphor production.
Using lexical functions to describe adjectives in terminography
Authors: Bonadonna Maria Francesca
Published: March 2020

The status of adjectives as independent terms has been demonstrated in recent studies. However, their treatment in
current terminography practice is not entirely satisfactory. This paper addresses the description of adjectives in term banks of
French adjectives related to the field of renewable energy. Our goals were to conduct a corpus-driven semantic analysis of a
sample of significant adjectives in this domain and to highlight some properties that should be taken into account in
terminography. In particular, we used lexical functions developed within the framework of Explanatory and Combinatorial
Lexicology. Our analysis shows that lexical functions are a powerful tool that can accurately define these adjectives, by showing
their subtle semantic distinctions. They are also able to capture the relations between the adjective and the noun that it
co-occurs with as well as systematically describe the paradigmatic and syntagmatic relations of adjectival terminological
units.
The use of English initialisms and abbreviations in the field of pharmaceutical business communication in
Spanish
Authors: Luján-García Carmen
Published: March 2020

The present paper deals with the use of English initialisms and abbreviations in the professional field of
pharmaceutical business communication in Spanish. This specialized area has not yet been previously examined, and the use of
initialisms and abbreviations is becoming more and more extended. The corpus consisted in an up-to-date list of thirty-seven
shortened forms, which was extracted from a digital magazine addressed to pharmacists. In order to document the use of the
initialisms, acronyms and abbreviations examined in Spanish, a combined analysis was carried out: firstly, the above mentioned
list of initialisms and acronyms from the online magazine www.correofarmaceutico.com provided evidence about their use in written language; and secondly, the
twenty-one pharmacists who answered our questionnaire provided data about practitioners’ familiarity with and the actual usage of
these lexical items.
Interplay between van der Waals and dipole–dipole interactions among Rydberg atoms
Authors: de Hond J , Cisternas Nataly , Spreeuw R J C , van Linden van den Heuvell H B , Druten N J van
Published: March 2020

Coherently manipulating Rydberg atoms in mesoscopic systems has proven challenging due to the unwanted population of nearby Rydberg levels by black-body radiation. Recently, there have been some efforts towards understanding these effects using states with a low principal quantum number that only have resonant dipole–dipole interactions. We perform experiments that exhibit black-body-induced dipole–dipole interactions for a state that also has a significant van der Waals interaction. Using an enhanced rate-equation model that captures some of the long-range properties of the dipolar interaction, we show that the initial degree of Rydberg excitation is dominated by the van der Waals interaction, while the observed linewidth at later times is dominated by the dipole–dipole interaction. We also point out some prospects for quantum simulation.
Complex electrical spiking activity in resistive switching nanostructured Au two-terminal devices
Authors: Mirigliano M , Decastri D , Pullia A , Dellasega D , Casu A , Falqui A , Milani P
Published: March 2020

Networks of nanoscale objects are the subject of increasing interest as resistive switching systems for the fabrication of neuromorphic computing architectures. Nanostructured films of bare gold clusters produced in gas phase with thickness well beyond the electrical percolation threshold, show a non-ohmic electrical behavior and resistive switching, resulting in groups of current spikes with irregular temporal organization. Here we report the systematic characterization of the temporal correlations between single spikes and spiking rate power spectrum of nanostructured Au two-terminal devices consisting of a cluster-assembled film deposited between two planar electrodes. By varying the nanostructured film thickness we fabricated two different classes of devices with high and low initial resistance respectively. We show that the switching dynamics can be described by a power law distribution in low resistance devices whereas a bi-exponential behavior is observed in the high resistance ones. The measured resistance of cluster-assembled films shows a

1
/

f

α

scaling behavior in the range of analyzed frequencies. Our results suggest the possibility of using cluster-assembled Au films as components for neuromorphic systems where a certain degree of stochasticity is required.
Two transitions in spatial modular networks
Authors: Gross Bnaya , Vaknin Dana , Buldyrev Sergey V , Havlin Shlomo
Published: March 2020

Understanding the resilience of infrastructures, such as a transportation network, has significant importance for our daily life. Recently, a homogeneous spatial network model was developed for studying spatial embedded networks with characteristic link length such as power-grids and the brain. However, although many real-world networks are spatially embedded and their links have characteristics length such as pipelines, power lines or ground transportation lines they are not homogeneous but rather heterogeneous. For example, density of links within cities are significantly higher than between cities. Here we develop and study numerically and analytically a similar realistic heterogeneous spatial modular model using percolation process to better understand the effect of heterogeneity on such networks. The model assumes that inside a city there are many lines connecting different locations, while long lines between the cities are sparse and usually directly connecting only a few nearest neighbours cities in a two dimensional plane. We find that ourheterogeneousmodel experiences two distinct continuous transitions, one when the cities disconnect from each other and the second when each city breaks apart. This is in contrast to thehomogeneousmodel where a single transition is found. Although the critical threshold for site percolation in 2D grid remains an open question we analytically find the critical threshold for site percolation in this model. In addition, it has been found that the homogeneous model experience a single transition having a unique phenomenon calledcritical stretchingwhere a geometric crossover from random to spatial structure in different scales found to stretch non-linearly with the characteristic length at criticality. In marked contrast, we show here that the heterogeneous model does not experience such a phenomenon indicating that critical stretching strongly depends on the network structure.
Influences of annealing temperature on properties of Fe2+:ZnSe thin films deposited by electron beam evaporation and their applications to Q-switched fiber laser*
Authors: Qing Du-Xin , Wang Shu-Tong , Ning Shou-Gui , Zhang Wei , Chen Xiao-Xu , Zhang Hong , Feng Guo-Ying , Zhou Shou-Huan
Published: March 2020

Fe2+:ZnSe thin films are prepared on sapphire substrate at room temperature by electron beam evaporation and then annealed in vacuum (about 1 × 10–4 Pa) at different temperatures. The influences of thermal annealing on the structural and optical properties of these films such as grain size and optical transmittance are investigated. The x-ray diffraction patterns show that the Fe2+:ZnSe thin film is preferred to be oriented along the (111) plane at different annealing temperatures. After the film is annealed, the full-width-at-half-maximum ( FWHM ) of the x-ray diffraction peak profile (111) of the film decreases and its crystal quality is improved. Scanning electron microscope images show that the films are more dense after being annealed. Finally, the sample is used as a saturable absorber in ZBLAN fiber laser. The annealed Fe2+:ZnSe thin films can be used to realize stable Q-switching modulation on ZBLAN fiber laser. The results demonstrate that the Fe2+:ZnSe thin film is a promising material for generating the high-power pulses of mid-infrared Q-switched fiber lasers.
Application of graphene vertical field effect to regulation of organic light-emitting transistors*
Authors: Song Hang , Wu Hao , Lu Hai-Yang , Yang Zhi-Hao , Ba Long
Published: March 2020

The luminescence intensity regulation of organic light-emitting transistor (OLED) device can be achieved effectively by the combination of graphene vertical field effect transistor (GVFET) and OLED. In this paper, we fabricate and characterize the graphene vertical field-effect transistor with gate dielectric of ion–gel film, confirming that its current switching ratio reaches up to 102. Because of the property of high light transmittance in ion–gel film, the OLED device prepared with graphene/PEDOT:PSS as composite anode exhibits good optical properties. We also prepare the graphene vertical organic light-emitting field effect transistor (GVOLEFET) by the combination of GVFET and graphene OLED, analyzing its electrical and optical properties, and confirming that the luminescence intensity can be significantly changed by regulating the gate voltage.
Phase separation and super diffusion of binary mixtures of active and passive particles*
Authors: Wang Yan , Shen Zhuanglin , Xia Yiqi , Feng Guoqiang , Tian Wende
Published: March 2020

Computer simulations were performed to study the dense mixtures of passive particles and active particles in two dimensions. Two systems with different kinds of passive particles (e.g., spherical particles and rod-like particles) were considered. At small active forces, the high-density and low-density regions emerge in both systems, indicating a phase separation. At higher active forces, the systems return to a homogeneous state with large fluctuation of particle area in contrast with the thermo-equilibrium state. Structurally, the rod-like particles accumulate loosely due to the shape anisotropy compared with the spherical particles at the high-density region. Moreover, there exists a positive correlation between Voronoi area and velocity of the particles. Additionally, a small number of active particles capably give rise to super-diffusion of passive particles in both systems when the self-propelled force is turned on.
Effect of transversal concentration gradient on H2–O2 cellular detonation*
Authors: Wang Cheng , Wu Yi-Xuan , Huang Jin , Han Wen-Hu , Song Qing-Guan
Published: March 2020

A two-dimensional detonation in H2–O2 system is simulated by a high-resolution code based on the fifth-order weighted essentially non-oscillatory (WENO) scheme in the spatial discretization and the 3th-order additive Runge–Kutta schemes in the time discretization, by using a detailed chemical model. The effect of a concentration gradient on cellular detonation is investigated. The results show that with the increase of the concentration gradient, the cell instability of detonation increases and gives rise to the oscillation of average detonation velocity. After a long time, for the case of the lower gradient the detonation can be sustained, with the multi-head mode and single-head mode alternating, while for the higher gradient it propagates with a single-head mode.
Efficient tensor decomposition method for noncircular source in colocated coprime MIMO radar*
Authors: Xie Qian-Peng , Pan Xiao-Yi , Xiao Shun-Ping
Published: March 2020

An effective method via tensor decomposition is proposed to deal with the joint direction-of-departure (DOD) and direction-of-arrival (DOA) estimation of noncircular sources in colocated coprime MIMO radar. By decomposing the transmitter and receiver into two sparse subarrays, noncircular property of source can be used to construct new extended received signal model for two sparse subarrays. The new received model can double the virtual array aperture due to the elliptic covariance of imping sources is nonzero. To further exploit the multidimensional structure of the noncircular received model, we stack the subarray output and its conjugation according to mode-1 unfolding and mode-2 unfolding of a third-order tensor, respectively. Thus, the corresponding extended tensor model consisted of noncircular information for DOA and DOD can be obtained. Then, the higher-order singular value decomposition technique is utilized to estimate the accurate signal subspace and angular parameter can be automatically paired via the rotational invariance relationship. Specifically, the ambiguous angle can be eliminated and the true targets can be achieved with the aid of the coprime property. Furthermore, a closed-form expression for the deterministic CRB under the NC sources scenario is also derived. Simulation results verify the superiority of the proposed estimator.
Location of micro-cracks in plates using time reversed nonlinear Lamb waves*
Authors: Liu Yaoxin , He Aijun , Liu Jiehui , Mao Yiwei , Liu Xiaozhou
Published: March 2020

A promising tool to detect micro-cracks in plate-like structures is used for generating higher harmonic Lamb waves. In this paper, a method combining nonlinear S0 mode Lamb waves with time reversal to locate micro-cracks is presented and verified by numerical simulations. Two different models, the contact acoustic nonlinearity (CAN) model and the Preisach–Mayergoyz (PM) model, are used to simulate a localized damage in a thin plate. Pulse inversion method is employed to extract the second and fourth harmonics from the received signal. Time reversal is performed to compensate the dispersion of S0 mode Lamb waves. Consequently, the higher harmonics generated from the damaged area can be refocused on their source. By investigating the spatial distribution of harmonic wave packets, the location of micro-cracks will be revealed. The numerical simulations indicate that this method gives accurate locations of the damaged area in a plate. Furthermore, the PM model is proved to be a suitable model to simulate the micro-cracks in plates for generation of higher harmonics.
Narrowband perfect terahertz absorber based on polar-dielectrics metasurface*
Authors: Zhao Meng-Meng , Fu Shu-Fang , Zhou Sheng , Song Yu-Ling , Zhang Qiang , Yin Yong-Qi , Zhao Yu-Tian , Liang Hong , Wang Xuan-Zhang
Published: March 2020

We theoretically propose a narrowband perfect absorber metasurface (PAMS) based on surface phonon polaritons in the terahertz range. The PAMS has unit cell consisting of a silver biarc on the top, a thin polar-dielectric in the middle and a silver layer at the bottom. The phonon polaritons are excited at the interface between the silver biarc and the polar dielectric, and enhance the absorption of the PAMS. The absorption peak is at 36.813 μm and the full width half maximum (FWHM) is nearly 36 nm, independent of the polarization and incidence angle. The electric fields are located at the split of the biarc silver layer and the quality factor Q is 1150. The FWHM decreases with the decreasing split width. When the thickness of the bottom layer is larger than 50 nm, the narrow band and high absorption are insensitive to the thickness of those layers. The designed absorber may have useful applications in terahertz spectra such as energy harvesting, thermal emitter, and sensing.
Improvements in reverse breakdown characteristics of THz GaAs Schottky barrier varactor based on metal-brim structure
Authors: Qi Lu-Wei , Liu Xiao-Yu , Meng Jin , Zhang De-Hai , Zhou Jing-Tao
Published: March 2020

The excellent reverse breakdown characteristics of Schottky barrier varactor (SBV) are crucially required for the application of high power and high efficiency multipliers. The SBV with a novel Schottky structure named metal–brim is fabricated and systemically evaluated. Compared with normal structure, the reverse breakdown voltage of the new type SBV improves from –7.31 V to –8.75 V. The simulation of the Schottky metal–brim SBV is also proposed. Three factors, namely distribution of leakage current, the electric field, and the area of space charge region are mostly concerned to explain the physical mechanism. Schottky metal–brim structure is a promising approach to improve the reverse breakdown voltage and reduce leakage current by eliminating the accumulation of charge at Schottky electrode edge.
Low temperature magnetism in the rare-earth perovskite GdScO3*
Authors: Sheng Jie-Ming , Kan Xu-Cai , Ge Han , Yuan Pei-Qian , Zhang Lei , Zhao Nan , Song Zong-Mei , Yao Yuan-Yin , Tang Ji-Ning , Wang Shan-Min , Tian Ming-Liang , Tong Xin , Wu Liu-Suo
Published: March 2020

The magnetic phase diagram of rare-earth perovskite compound, GdScO3, has been investigated by magnetization and heat capacity. The system undergoes an antiferromagnetic phase transition at T
N = 2.6 K, with an easy axis of magnetization along the a axis. The magnetization measurements show that it exists a spin-flop transition around 0.3 T for the applied field along the a axis. The critical magnetic field for the antiferromagnetic-to-paramagnetic transition is near 3.2 T when temperature approaches zero. By scaling susceptibilities, we presume this point (B = 3.2 T, T = 0 K) might be a field-induced quantum critical point and the magnetic critical fluctuations can even be felt above T
N.
Topological Anderson insulator in two-dimensional non-Hermitian systems*
Authors: Liu Hongfang , Su Zixian , Zhang Zhi-Qiang , Jiang Hua
Published: March 2020

We study the disorder-induced phase transition in two-dimensional non-Hermitian systems. First, the applicability of the noncommutative geometric method (NGM) in non-Hermitian systems is examined. By calculating the Chern number of two different systems (a square sample and a cylindrical one), the numerical results calculated by NGM are compared with the analytical one, and the phase boundary obtained by NGM is found to be in good agreement with the theoretical prediction. Then, we use NGM to investigate the evolution of the Chern number in non-Hermitian samples with the disorder effect. For the square sample, the stability of the non-Hermitian Chern insulator under disorder is confirmed. Significantly, we obtain a nontrivial topological phase induced by disorder. This phase is understood as the topological Anderson insulator in non-Hermitian systems. Finally, the disordered phase transition in the cylindrical sample is also investigated. The clean non-Hermitian cylindrical sample has three phases, and such samples show more phase transitions by varying the disorder strength: (1) the normal insulator phase to the gapless phase, (2) the normal insulator phase to the topological Anderson insulator phase, and (3) the gapless phase to the topological Anderson insulator phase.
Propagation properties of radially polarized Pearcey-Gauss vortex beams in free space*
Authors: Chen Xinpeng , Xu Chuangjie , Yang Qian , Luo Zhiming , Li Xixian , Deng Dongmei
Published: March 2020

We investigate a family of radially polarized Pearcey–Gauss vortex beams (RPPGVBs), obtain the general propagation expressions of an RPPGVB, and study the intensity distribution, phase pattern, spin currents as well as the orbital currents when the RPPGVB propagates in free space. The focal plane and the intensity of the focal point can be adjusted by changing the position of the vortex and the scaling factors. We also investigate how the waist size influences the propagation properties.
Exploration and elaboration of photo-induced proton transfer dynamical mechanism for novel 2-[1,3]dithian-2-yl-6-(7aH-indol-2-yl)-phenol sensor*
Authors: Xu Lei , Zhang Tian-Jie , Zhang Qiao-Li , Yang Da-Peng
Published: March 2020

In this work, we theoretically probe into the photo-induced hydrogen bonding effects between S0 state and S1 state as well as the excited state intramolecular proton transfer (ESIPT) behavior for a novel 2-[1,3]dithian-2-yl-6-(7 aH-indol-2-yl)-phenol (DIP) probe system. We first study the ground-state hydrogen bonding O–H⋯N behavior for DIP. Then we analyze the primary geometrical parameters (i.e., bond length, bond angle, and infrared (IR) stretching vibrational mode) involved in hydrogen bond, and confirm that the O–H⋯N of DIP should be strengthened in the first excited state. It is the significant prerequisite for ESIPT reaction. Combining the frontier molecular orbitals (MOs) with vertical excitation analyses, the intramolecular charge transfer (ICT) phenomenon can be found for the DIP system, which reveals that the charge redistribution facilitates ESIPT behavior. By constructing potential energy curves for DIP along the ESIPT reactional orientation, we obtain quite a small energy barrier (3.33 kcal/mol) and affirmed that the DIP molecule undergoes ultrafast ESIPT process once it is excited to the S1 state and quickly transfers its proton, forming DIP-keto tautomer. That is why no fluorescence of DIP can be observed in experiment, which further reveals the ultrafast ESIPT mechanism proposed in this work.
Magnetic field enhanced single particle tunneling in MoS2–superconductor vertical Josephson junction*
Authors: Xu Wen-Zheng , Qin Lai-Xiang , Ye Xing-Guo , Lin Fang , Yu Da-Peng , Liao Zhi-Min
Published: March 2020

As a prototypical transition-metal dichalcogenide semiconductor, MoS2 possesses strong spin–orbit coupling, which provides an ideal platform for the realization of interesting physical phenomena. Here, we report the magnetotransport properties in NbN–MoS2–NbN sandwich junctions at low temperatures. Above the critical temperature around ∼11 K, the junction resistance shows weak temperature dependence, indicating a tunneling behavior. While below ∼11 K, nearly zero junction resistance is observed, indicating the superconducting state in the MoS2 layer induced by the superconducting proximity effect. When a perpendicular magnetic field ∼1 T is applied, such proximity effect is suppressed, accompanying with insulator-like temperature-dependence of the junction resistance. Intriguingly, when further increasing the magnetic field, the junction conductance is significantly enhanced, which is related to the enhanced single particle tunneling induced by the decrease of the superconducting energy gap with increasing magnetic fields. In addition, the possible Majorana zero mode on the surface of MoS2 can further lead to the enhancement of the junction conductance.
Phase-modulated quadrature squeezing in two coupled cavities containing a two-level system*
Authors: Li Hao-Zhen , Zeng Ran , Zhou Xue-Fang , Bi Mei-Hua , Xu Jing-Ping , Yang Ya-Ping
Published: March 2020

The phase-modulated quadrature squeezing in the system that composed of two coupled cavities interacting with a two-level atom is investigated. The variances of the amplitude and phase quadrature of the output field are calculated. It turns out that the squeezing behaviors of the output field can be obviously modified due to the phase difference of the coupling strengths between the atom and the two cavities. The squeezing in one quadrature (i.e., phase quadrature) can be transferred into another (i.e., amplitude quadrature), or the quadrature squeezing located at the low-frequency region can be transferred into the high-frequency region by modulating the relative phase of the coupling strengths. Furthermore, the effects of the decay mismatch between the two cavities and the coupling mismatch between the atom and the cavities on the quadrature squeezing have been discussed. The results show that both the decay mismatch and the coupling mismatch play a positive role in generating better quadrature squeezing.
Bose–Einstein condensates in an eightfold symmetric optical lattice*
Authors: Niu Zhen-Xia , Tai Yong-Hang , Shi Jun-Sheng , Zhang Wei
Published: March 2020

We investigate the properties of Bose–Einstein condensates (BECs) in a two-dimensional quasi-periodic optical lattice (OL) with eightfold rotational symmetry by numerically solving the Gross–Pitaevskii equation. In a stationary external harmonic trapping potential, we first analyze the evolution of matter-wave interference pattern from periodic to quasi-periodic as the OL is changed continuously from four-fold periodic to eight-fold quasi-periodic. We also investigate the transport properties during this evolution for different interatomic interaction and lattice depth, and find that the BEC crosses over from ballistic diffusion to localization. Finally, we focus on the case of eightfold symmetric lattice and consider a global rotation imposed by the external trapping potential. The BEC shows vortex pattern with eightfold symmetry for slow rotation, becomes unstable for intermediate rotation, and exhibits annular solitons with approximate axial symmetry for fast rotation. These results can be readily demonstrated in experiments using the same configuration as in Phys. Rev. Lett.
122 110404 (2019).
Ergodicity recovery of random walk in heterogeneous disordered media*
Authors: Luo Liang , Yi Ming
Published: March 2020

Significant and persistent trajectory-to-trajectory variance are commonly observed in particle tracking experiments, which have become a major challenge for the experimental data analysis. In this theoretical paper we investigate the ergodicity recovery behavior, which helps clarify the origin and the convergence of trajectory-to-trajectory fluctuation in various heterogeneous disordered media. The concepts of self-averaging and ergodicity are revisited in the context of trajectory analysis. The slow ergodicity recovery and the non-Gaussian diffusion in the annealed disordered media are shown as the consequences of the central limit theorem in different situations. The strange ergodicity recovery behavior is reported in the quenched disordered case, which arises from a localization mechanism. The first-passage approach is introduced to the ergodicity analysis for this case, of which the central limit theorem can be employed and the ergodicity is recovered in the length scale of diffusivity correlation.
Electronic structure and phase transition engineering in NbS2: Crucial role of van der Waals interactions*
Authors: Wang Wei , Lei Wen , Zheng Xiaojun , Li Huan , Tang Xin , Ming Xing
Published: March 2020

Based on first-principles simulations, we revisit the crystal structures, electronic structures, and structural stability of the layered transition metal dichalcogenides (TMDCs) NbS2, and shed more light on the crucial roles of the van der Waals (vdW) interactions. Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure, which is significant to correctly describe the electronic structure of NbS2. More interestingly, under hydrostatic pressure or tensile strain in ab plane, an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the I4/mmm phase has been uncovered. The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects. The interlayer Nb–S distances collapse and the interlayer vdW interactions disappear, concomitant with new covalent bond emerging and increasing coordination number. Present work highlights the significance of the vdW interactions, and provides new insights on the unconventional structural transitions in NbS2, which will attract wide audience working in the hectic field of TMDCs.
Raman scattering study of two-dimensional magnetic van der Waals compound VI3
*
Authors: Wang Yi-Meng , Tian Shang-Jie , Li Cheng-He , Jin Feng , Ji Jian-Ting , Lei He-Chang , Zhang Qing-Ming
Published: March 2020

The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research. Previous x-ray diffraction (XRD) studies on the magnetic van der Waals compound VI3, revealed a structural transition above the magnetic transition but output controversial analysis on symmetry. In this paper we carried out polarized Raman scattering measurements on VI3 from 10 K to 300 K, with focus on the two A
g phonon modes at ∼ 71.1 cm−1 and 128.4 cm−1. Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by C
2h
rather than D
3d
both above and below structural phase transition. We further performed temperature-dependent Raman experiments to study the magnetism in VI3. Fano asymmetry and anomalous linewidth drop of two A
g phonon modes at low temperatures, point to a significant spin–phonon coupling. This is also supported by the softening of 71.1-cm−1 mode above the magnetic transition. The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI3. And spin–phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.
Parametric study of the clustering transition in vibration driven granular gas system*
Authors: Wu Qi-Lin , Hou Mei-Ying , Yang Lei , Wang Wei , Yang Guang-Hui , Tao Ke-Wei , Chen Liang-Wen , Zhang Sheng
Published: March 2020

A parametric study of the clustering transition of a vibration-driven granular gas system is performed by simulation. The parameters studied include the global volume fraction of the system, the size of the system, the friction coefficient, and the restitution coefficient among particles and among particle–walls. The periodic boundary and fixed boundary of sidewalls are also checked in the simulation. The simulation results provide us the necessary “heating” time for the system to reach steady state, and the friction term needed to be included in the “cooling” time. A gas-cluster phase diagram obtained through Kolmogorov–Smirnov (K–S) test analysis using similar experimental parameters is given. The influence of the parameters to the transition is then investigated in simulations. This simulation investigation helps us gain understanding which otherwise cannot be obtained by experiment alone, and makes suggestions on the determination of parameters to be chosen in experiments.
Semi-integer harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized laser field*
Authors: Qi Tong , Huo Xiao-Xin , Zhang Jun , Liu Xue-Shen
Published: March 2020

We theoretically investigated the properties of the high-order harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized (BCCP) laser field. The harmonic emission processes have been illustrated by numerically solving the two-dimensional time-dependent Schrödinger equation of an atom in intense laser fields. It is found that with the decrease of the right-circularly polarized laser wavelength, the harmonic spectra are gradually splitting and the harmonic orders move towards the higher frequency. Meanwhile, the integer and semi-integer harmonic emission will be generated when the frequency ratios of right- and left-circularly polarized lasers are semi-integer. The emission mechanism of the semi-integer-order harmonics has been investigated by using the rules of photon absorption and emission.
Finite-field calculation of electric quadrupole moments of 2P3/2, 2D3/2,5/2, and 2F5/2,7/2 states for Yb+ ion*
Authors: Guo Xi-Tong , Yu Yan-Mei , Liu Yong , Suo Bing-Bing
Published: March 2020

Electric quadrupole moments of low-lying excited states of Yb+ are calculated by relativistic coupled-cluster theory with perturbations from external fields. The field-dependent energy differentiation provides accurate values of the electric quadrupole moments of 2P3/2, 2D3/2,5/2, and 2F5/2,7/2 states which agree well with experimental values. The important role of the electronic correlation to the electric quadrupole moments is investigated. Our calculations indicate the early dispute of the electric quadrupole moment of the Yb+(2F7/2) state for which the measured and theoretical values have a large discrepancy. These electric quadrupole moment values can help us to determine the electric quadrupole shifts in start-of-the-art experiments of the Yb+ ion.
Single-shot measurement of THz pulses*
Authors: Yang Lei , Hou Lei , Dong Chengang , Shi Wei
Published: March 2020

Terahertz (THz) waves have shown a broad prospect in the analysis of some dielectric materials because of their special properties. For the ultrafast irreversible processes, the THz single-shot measurement is a good choice. In this paper, a single-shot system is investigated, where a pump beam is used to generate THz pulses with high electrical field by optical rectification in LiNbO3, the probe beam with wavefront tilted by a blazed grating is used for single-shot measurement. The time window is up to 90 ps, the signal to noise ratio is 2000 : 1, the spectrum covers from 0.1 THz to about 2.0 THz, and the spectral resolution is 0.011 THz. The single-shot measurement result agrees well with that of a traditional electrical-optic sampling method.