The higher-order rogue wave (RW) for a spatial discrete Hirota equation is investigated by the generalized (1,$N-1$)-fold Darboux transformation. We obtain the higher-order discrete RW solution to the spatial discrete Hirota equation. The fundamental RWs exhibit different amplitudes and shapes associated with the spectral parameters. The higher-order RWs display triangular patterns and pentagons with different peaks. We show the differences between the RW of the spatially discrete Hirota equation and the discrete nonlinear Schrödinger equation. Using the contour line method, we study the localization characters including the length, width, and area of the first-order RWs of the spatially discrete Hirota equation.

We propose and discuss a novel concept of robust set stabilization by permissible controls; this concept is helpful when dealing with both a priori information of model parameters and different permissible controls including quantum measurements. Both controllability and stabilization can be regarded as the special case of the novel concept. An instance is presented for a kind of uncertain open quantum systems to further justify this generalized concept. It is underlined that a new type of hybrid control based on periodically perturbed projective measurements can be the permissible control of uncertain open quantum systems when perturbed projective measurements are available. The sufficient conditions are given for the robust set stabilization of uncertain quantum open systems by the hybrid control, and the design of the hybrid control is reduced to selecting the period of measurements.

Considering the ocean water's optical attenuation and the roughness of the sea surface, we analyze the security of continuous-variable (CV) quantum key distribution (QKD) based air-to-water channel. The effects of the absorption and scattering on the transmittance of underwater quantum channel and the maximum secure transmission distance are studied. Considering the roughness of the sea surface, we simulate the performance bounds of CV QKD with different wind speeds using the Monte Carlo method. The results show that even if the secret key rate gradually reduces as the wind speed increases, the maximum transmission distance will not be affected obviously. Compared to the works regarding short-distance underwater optical communication, our research represents a significant step towards establishing secure communication between air platform and submarine vehicle.

We present a two-photon interference experiment in a modified Mach-Zehnder (MZ) interferometer in which two Hong–Ou–Mandel effects occur in tandem and construct superposed two-photon states. The signal photons pass both the arms of the MZ interferometer while the idler photons pass one arm only. Interestingly, the probability of the idler photons emerging from any output port still shows a sine oscillation with the two-photon phase difference and it can be characterized only by the indistinguishability of the two-photon amplitudes. We also observe a two-photon interference pattern with a period being equal to the wavelength of the parametric photons instead of the two-photon photonic de Broglie wavelength due to the presence of two-photon phase difference, in particular, with complementary probabilities of finding the two-photon pairs in two output ports. The abundant observations can facilitate a more comprehensive understanding of the two-photon interference.

To describe the energy-dependent characteristics of the reaction-subdiffusion process, we analyze the simple reaction A$\rightarrow $B under subdiffsion with waiting time depending on the preceding jump length, and derive the corresponding master equations in the Fourier–Laplace space for the distribution of A and B particles in a continuous time random walk scheme. Moreover, the generalizations of the reaction-diffusion equation for the Gaussian jump length with the probability density function of waiting time being quadratically dependent on the preceding jump length are obtained by applying the derived master equations.

Information encoding plays a crucial role in neuroscience. One of the fundamental questions in cognitive neuroscience is how the brain encodes external stimuli in the sensory cortex. We use a network model based on the Hodgkin–Huxley type to study the information transmitting including its storage and recall. The model is inspired by psychological and neurobiological evidence on sequential memories. The model contains excitatory and inhibitory neurons with all-to-all connections whose architecture has two layers. A lower layer represents consecutive events during the information encoding process, and the upper layer is used to tag sequences of events represented in the lower layer. The spike-timing-dependent plasticity learning rule is used for sequential storage of excitatory connections between the modules. Computer simulations demonstrate that the synchronization status of multiple neurons is dependent on the network connectivity patterns, and also this model has good performance for different sequences of storage and recall.

A prototype of a laser driven proton accelerator is built at Peking University. Protons exceeding 10 MeV are accelerated from micrometer-thick aluminum targets irradiated by tightly focused laser pulse with 1.8 J energy and 30 fs duration. The beam energy spectrum and charge distribution are measured by a Thomson parabola spectrometer and radiochromic film stacks. The sensitivity of proton cut-off energy to the focusing of the laser beam, the pulse duration, and the foil thickness are systematically investigated in the experiments. Stable proton beams have been produced with an optimized parameter set, providing a cornerstone for the future applications of laser accelerated protons.

Double resonance optical pumping spectroscopy has an outstanding advantage of high signal-to-noise ratio, thus having potential applications in precision measurement. With the counter propagated 780 nm and 776 nm laser beams acting on a rubidium vapor cell, the high resolution spectrum of $5S_{1/2}-5P_{3/2}-5D_{5/2}$ ladder-type transition of $^{87}$Rb atoms is obtained by monitoring the population of the $5S_{1/2}$ ground state. The dependence of the spectroscopy lineshape on the probe and coupling fields are comprehensively studied in theory and experiment. This research is helpful for measurement of fundamental physical constants by high resolution spectroscopy.

Generation of attosecond electromagnetic (EM) pulses and the associated electron dynamics are studied using particle-in-cell simulations of relativistic laser pulses interacting with over-dense plasma foil targets. The interaction process is found to be so complicated even in the situation of utilizing driving laser pulses of only one cycle. Two electron bunches closely involved in the laser-driven wavebreaking process contribute to attosecond EM pulses through the coherent synchrotron emission process whose spectra are found to follow an exponential decay rule. Detailed investigations of electron dynamics indicate that the early part of the reflected EM emission is the high-harmonics produced through the relativistic oscillating mirror mechanism. High harmonics are also found to be generated through the Bremsstrahlung radiation by one electron bunch that participates in the wavebreaking process and decelerates when it experiences the local wavebreaking-generated high electrostatic field in the moving direction.

Single crystal Er:LuAl$_{3}$(BO$_{3}$) (Er:LuAB) is successfully grown using the top-seeded solution growth method with a $K_{2}$Mo$_{3}$O$_{10}$ flux. The cell parameters of the grown crystal are estimated by an x-ray single crystal diffactometor and x-ray powder diffraction analysis. The result indicates that it still belongs to the space group $R32$. The obtained unit-cell parameters are $a=9.2793(19)$ Å, $c=7.210(3)$ Å, $V=537.65(27)$ Å$^{3}$, and $Z=3$. The absorption spectrum is measured at room temperature. The spectroscopy properties are investigated based on the Judd–Ofelt (J-O) theory, and the effective J-O parameters were calculated to be ${\it \Omega}_{2}=8.33\times10^{-20}$, ${\it \Omega}_{4}= 3.83\times10^{-20}$, and ${\it \Omega}_{6}=3.55\times10^{-20}$. The emission spectra of Er:LuAB crystal at room temperature are also studied and the $^{4}I_{11/2}\to {}^{4}I_{13/2}$ fluorescence around 3170 nm is observed. The emission cross section calculated by the F-L formula is $8.6\times10^{-20}$ cm$^{2}$. These results suggest that the Er:LuAB crystal may be a promising $\sim$3 μm laser material.

Metallic nanoparticle (NP) shapes have a significant influence on the property of composite embedded with metallic NPs. Swift heavy ion irradiation is an effective way to modify shapes of metallic NPs embedded in an amorphous matrix. We investigate the shape deformation of Ag NPs with irradiation fluence, and 357 MeV Ni ions are used to irradiate the silica containing Ag NPs, which are prepared by ion implantation and vacuum annealing. The UV-vis results show that the surface plasmon resonance (SPR) peak from Ag NPs shifts from 400 to 377 nm. The SPR peak has a significant shift at fluence lower than $1\times10^{14}$ ions/cm$^{2}$ and shows less shift at fluence higher than $1\times10^{14}$ ions/cm$^{2}$. The TEM results reveal that the shapes of Ag NPs also show significant deformation at fluence lower than $1\times10^{14}$ ions/cm$^{2}$ and show less deformation at fluence higher than $1\times10^{14}$ ions/cm$^{2}$. The blue shift of the SPR peak is considered to be the consequence of defect production and Ag NP shape deformation. Based on the thermal spike model calculation, the temperature of the silica surrounding Ag particles first increases rapidly, then the region of Ag NPs close to the interface of Ag/silica is gradually heated. Therefore, the driven force of Ag NPs deformation is considered as the volume expansion of the first heated silica layer surrounding Ag NPs.

Microstructural evolution in H-implanted polycrystalline $\alpha$-SiC upon thermal annealing at temperature 1100${^\circ}$C is studied. After annealing, the samples are examined via cross-sectional transmission electron microscopy (XTEM) analysis. H$_{2}$ gas bubbles are formed during H implantation and some H$_{2}$ molecules are released from the bubble to form cavities during thermal annealing. The distribution and size of the observed cavities are related to the implantation fluence. The results are compared to H implanted single crystal SiC and He implanted polycrystalline $\alpha$-SiC. The possible reasons are discussed.

The Sb$_{6}$Te$_{4}$/VO$_{2}$ multilayer thin films are prepared by magnetron sputtering and the potential application in phase change memory is investigated in detail. Compared with Sb$_{6}$Te$_{4}$, Sb$_{6}$Te$_{4}$/VO$_{2}$ multilayer composite thin films have higher phase change temperature and crystallization resistance, indicating better thermal stability and less power consumption. Also, Sb$_{6}$Te$_{4}$/VO$_{2}$ has a broader energy band of 1.58 eV and better data retention (125$^{\circ}\!$C for 10 y). The crystallization is suppressed by the multilayer interfaces in Sb$_{6}$Te$_{4}$/VO$_{2}$ thin film with a smaller rms surface roughness for Sb$_{6}$Te$_{4}$/VO$_{2}$ than monolayer Sb$_{4}$Te$_{6}$. The picosecond laser technology is applied to study the phase change speed. A short crystallization time of 5.21 ns is realized for the Sb$_{6}$Te$_{4}$(2 nm)/VO$_{2}$ (8 nm) thin film. The Sb$_{6}$Te$_{4}$/VO$_{2}$ multilayer thin film is a potential and competitive phase change material for its good thermal stability and fast phase change speed.

Non-stoichiometry effect on the extreme magnetoresistance is systematically investigated for the Weyl semimetal WTe$_{2}$. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fits to a two-band model show that the magnetoresistance is strongly dependent on the residual resistivity ratio (i.e., the degree of non-stoichiometry), which is eventually understood in terms of electron doping that not only breaks the balance between electron-type and hole-type carrier densities, but also reduces the average carrier mobility. Thus the compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe$_{2}$.

We have utilized second harmonic generation (SHG) to disentangle the coupled first-order charge order/structural transition at $T_{\rm c}\sim281$ K in the transition-metal dichalocogenide IrTe$_{2}$, an exceptional layered material with 3D properties. The data from SHG shows extremely sharp transition in both the cooling and warming processes with less than 0.2 K transition window. Surface electronic symmetries of $C_{3v}$ and $S_{2}$ are observed in the high temperature and low temperature phases, respectively. Compared to neutron diffraction data for the structural transition (Phys. Rev. B 88 (2013) 115122) and to the electrical resistivity for the microscopic transition (Phys. Rev. B 95 (2017) 035148), our data indicates the electronic transition at the surface is the precursor to the structural transition.

A parallel-coupled double quantum dot (PCDQD) system with two multi-quantum dot chains is designed. Conductance versus Fermi energy level is investigated utilizing the non-equilibrium Green's function approach. If two quantum dots are added on each side of the PCDQD system, additional Breit–Wigner and Fano resonances occur in the conductance spectra. If quantum dots are added on one side of the system, small Fano resonances can be observed in the conductance spectra. Adjusting the number of side-coupled quantum dots, the anti-resonance bands emerge at different positions, which makes the system applicable as a quantum switching device. Moreover, the $I$–$V$ characteristic curve presents the step characteristic and the width of the step decreases with increasing the number of side-coupled quantum dots.

Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO$_{3}$ bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptors. The formation energies show that cation vacancies are energetically favorable in bulk LaAlO$_{3}$ under O-rich conditions, while the Al$_{\rm La}$ antisites are stable in reducing atmosphere. However, the same behavior does not appear in the case of LaAlO$_{3}$ films. For LaO-terminated LaAlO$_{3}$ films, La or Al vacancies remain energetically favorable under O-rich and O-deficient conditions. For an AlO$_{2}$-terminated surface, under O-rich condition the La interstitial atom is repelled from the outmost layer after optimization, which releases more stress leading to the decrease of total energy of the system. An Al interstitial atom has a smaller radius so that it can stay in distorted films and becomes more stable under O-deficient conditions, and the Al interstitial atoms can be another possible carrier source contribution to the conductivity of n-type interface under an ultrahigh vacuum. La and Al antisites have similar formation energy regardless of oxygen pressure. The results would be helpful to understand the defect structures of LaAlO$_{3}$-related materials.

Devices of electric double-layer transistors (EDLTs) with ionic liquid have been employed as an effective way to dope carriers over a wide range. However, the induced electronic states can hardly survive in the materials after releasing the gate voltage $V_{\rm G}$ at temperatures higher than the melting point of the selected ionic liquid. Here we show that a permanent superconductivity with transition temperature $T_{\rm c}$ of 24 and 15 K is realized in single crystals and polycrystalline samples of HfNCl and ZrNCl upon applying proper $V_{\rm G}$'s at different temperatures. Reversible change between insulating and superconducting states can be obtained by applying positive and negative $V_{\rm G}$ at low temperature such as 220 K, whereas $V_{\rm G}$'s applied at 250 K induce the irreversible superconducting transition. The upper critical field $H_{\rm c2}$ of the superconducting states obtained at different gating temperatures shows similar temperature dependence. We propose a reasonable scenario that partial vacancy of Cl ions could be caused by applying proper $V_{\rm G}$'s at slightly higher processing temperatures, which consequently results in a permanent electron doping in the system. Such a technique shows great potential to systematically tune the bulk electronic state in the similar two-dimensional systems.

Metal organic chemical vapor deposition (MOCVD) growth systems are one of the main types of equipment used for growing single crystal materials, such as GaN. To obtain film epitaxial materials with uniform performance, the flow field and temperature field in a GaN-MOCVD reactor are investigated by modeling and simulating. To make the simulation results more consistent with the actual situation, the gases in the reactor are considered to be compressible, making it possible to investigate the distributions of gas density and pressure in the reactor. The computational fluid dynamics method is used to study the effects of inlet gas flow velocity, pressure in the reactor, rotational speed of graphite susceptor, and gases used in the growth, which has great guiding significance for the growth of GaN film materials.

The excited-state double-proton transfer (ESDPT) mechanism of 2-amino-3-methoxypyridine and acetic acid complex is studied by the density functional theory (DFT) and time-dependent DFT with CAM-B3LYP functional. The complex is connected through two different types of inter-molecular hydrogen bonds. After photo-excitation, both hydrogen bonds get strengthened, which can facilitate the ESDPT reaction. The scanned potential energy curve along the proton transfer coordinate indicates that the ESDPT reaction proceeds in a stepwise pattern.

Effect of hydrogen (H$_2$) treatment during the GaN barrier growth on the electroluminescence performance of green InGaN/GaN single-quantum-well light-emitting diodes (LEDs) grown on Si substrates is experimentally investigated. We prepare two LED samples with different carrier gas compositions during the growth of GaN barrier. In the H$_2$ free LED, the GaN barrier is grown in full nitrogen (N$_2$) atmosphere. For the other H$_2$ treated LED, a mixture of N$_2$ and H$_2$ was used as the carrier gas. It is observed that V-shaped pits decrease in size after H$_2$ treatment by means of the scanning electron microscope. Due to the fact that the p-n junction interface would be closer to the p-GaN as a result of smaller V-shaped pits, the tunneling barrier for holes to inject into the InGaN quantum well would become thicker after H$_2$ treatment. Hence, the external quantum efficiency of the H$_2$ treated LED is lower compared to the H$_2$ free LED. However, LEDs would exhibit a better leakage behavior after H$_2$ treatment during the GaN barrier growth because of more effective blocking of the threading dislocations as a result of the H$_2$ etching at V-shaped pits.

The transfer characteristics of amorphous indium-zinc-oxide thin film transistors are measured in the temperature range of 10–400 K. The variation of electrical parameters (threshold voltage, field effect mobility, sub-threshold swing, and leakage current) with decreasing temperature are then extracted and analyzed. Moreover, the dominated carrier transport mechanisms at different temperature regions are investigated. The experimental data show that the carrier transport mechanism may change from trap-limited conduction to variable range hopping conduction at lower temperature. Moreover, the field effect mobilities are also extracted and simulated at various temperatures.

We investigate how the way of breaking links and establishing links impacts cooperation by comparing four coevolutionary rules. In the rules, a player chooses to break an existing link according to his environment, and the establishment of a new link depends on the environment of the potential neighbor. It is found that the way of breaking links plays a key role in promoting cooperation. The way of establishing links has a negligible effect on cooperation, but determines the population structure. Our results may provide some insights into understanding the evolution of cooperation.

We present the interior solutions of distributions of magnetized fluid inside a sphere in $f(R,T)$ gravity. The magnetized sphere is embedded in an exterior Reissner–Nordström metric. We assume that all physical quantities are in static equilibrium. The perfect fluid matter is studied under a particular form of the Lagrangian density $f(R,T)$. The magnetic field profile in modified gravity is calculated. Observational data of neutron stars are used to plot suitable models of magnetized compact objects. We reveal the effect of $f(R,T)$ gravity on the magnetic field profile, with application to neutron stars, especially highly magnetized neutron stars found in x-ray pulsar systems. Finally, the effective potential $V_{\rm eff}$ and innermost stable circular orbits, arising out of the motion of a test particle of negligible mass influenced by attraction or repulsion from the massive center, are discussed.