Breathers and rogue waves as exact solutions of the three-dimensional Kadomtsev–Petviashvili equation are obtained via the bilinear transformation method. The breathers in three dimensions possess different dynamics in different planes, such as growing and decaying periodic line waves in the $(x,y)$, $(x,z)$ and $(y,t)$ planes. Rogue waves are localized in time, and are obtained theoretically as a long wave limit of breathers with indefinitely larger periods. It is shown that the rogue waves possess growing and decaying line profiles in the $(x,y)$ or $(x,z)$ plane, which arise from a constant background and then retreat back to the same background again.

We investigate the structure-preserving numerical algorithm of the Degasperis–Procesi equation which can be transformed into a bi-Hamiltonian form using the discrete variational derivative method. Based on two different space discretization methods, the Fourier pseudospectral method and the wavelet collocation method, we develop two modified structure-preserving schemes under the periodic boundary condition. These proposed schemes are proved to preserve the Hamiltonian invariants theoretically and numerically. Meanwhile, the numerical results confirm that they can simulate the propagation of solitons effectively for a long time.

The exact solutions of a chain of type II are investigated. The chain of type II is first transformed to an integrable differential-difference equation, which has the Kaup–Newell spectral problem as its continuous spatial spectral problem and a Darboux transformation of the Kaup–Newell equation as its discrete temporal spectral problem. Then, with these spectral problems, a Darboux transformation of the transformed equation is constructed. Finally, as an application of the Darboux transformation, an exact solution of the transformed equation and thus the chain of type II are presented.

We investigate the stability and collision dynamics of dissipative matter-wave solitons formed in a quasi-one-dimensional Bose–Einstein condensate with linear gain and three-body recombination loss perturbed by a weak optical lattice. It is shown that the linear gain can modify the stability of the single dissipative soliton moving in the optical lattice. The collision dynamics of two individual dissipative matter-wave solitons explicitly depend on the linear gain parameter, and they display different dynamical behaviors in both the in-phase and out-of-phase interaction regimes.

Based on Dirac's representation theory and the technique of integration within an ordered product of operators, we put forward the joint wavelet-fractional Fourier transform in the context of quantum mechanics. Its corresponding transformation operator is found and the normally ordered form is deduced. This kind of transformation may be applied to analyzing and identifying quantum states.

We introduce the deformed boson operators which satisfy a deformed boson algebra in some special types of generalized noncommutative phase space. Based on the deformed boson algebra, we construct coherent state representations. We calculate the variances of the coordinate operators on the coherent states and investigate the corresponding Heisenberg uncertainty relations. It is found that there are some restriction relations of the noncommutative parameters in these special types of noncommutative phase space.

We investigate the particle-hole fluctuation correction to the specific heat of an ultracold Fermi gas at unitarity within the framework of the non-self-consistent T-matrix approximation in the normal phase. We find good agreement between our theoretical predictions and the experimental data measured by the MIT group, apart from discrepancies near the transition temperature. At high temperature, our calculated specific heat has the tendency to approach the specific heat of the Boltzmann gas.

The convex hull on three points in two-dimensional Euclidean space of three flat edges (trihedron) is studied. The Bohr–Sommerfeld quantization of the area of space is performed. It is shown that it reproduces exactly the equidistant spacing spectrum found elsewhere.

The deconfinement phase transition with external magnetic field is investigated in the Friedberg–Lee model. We expand the potential around the two local minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group. By solving the flow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement.

We experimentally observe the high resolution direct frequency comb spectroscopy using counter-propagating broadband femtosecond pulses on two-photon transitions in room-temperature $^{87}$Rb atoms. The Doppler broadened background is effectively eliminated with the pulse shaping method and the spectrum modulation technique. The combination of the pulse shaping method and the spectra modulation technique provides a potential approach to reduce background of at least 99%.

We investigate the dipole–dipole broadened selective reflection spectrum with the Cs atomic density of $10^{14}$–10$^{15}$ cm$^{-3}$. The dipole–dipole broadening is reduced and the hyperfine splitting is well resolved when the ground state atoms are excited by a detuned pump beam. The dependences of dipole–dipole broadening of Cs atoms in the $6S_{1/2}(F=3)\rightarrow6P_{3/2}(F'=4)$ hyperfine transition line on atomic density and the excitation factor are studied. It is found that the reduction of the dipole–dipole broadening is dependent on the pump beam power and is independent of the atomic density in this density range. These results are useful for understanding of the dynamical process in this range of atomic density.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

We demonstrate the generation of passive mode-locked double-clad ytterbium-doped fiber laser operating in a 1-micron region. We prepare the saturable absorber from commercial crystal of molybdenum disulphide (MoS$_{2}$). Without chemical procedure, the MoS$_{2}$ is mechanically exfoliated by using a clear scotch tape. A few layers of MoS$_{2}$ flakes are obtained on the tape. Then, a piece of $1\times1$ mm tape containing MoS$_{2}$ thin flakes is inserted between two fiber ferrules and is integrated in the ring cavity. Stable mode-locking operation is attained at 1090 nm with a repetition rate of 13.2 MHz. Our mode-locked laser has a maximum output power of 20 mW with 1.48 nJ pulse energy. These results validate that the MoS$_{2}$ has a broad operating wavelength which covers the 1-micron region, and it is also able to work in a high-power cavity.

We demonstrate optical-carrier transfer over a 112-km single-span urban fiber link. By actively compensating the phase noise induced along the fiber link, a noise suppression of 55 dB at 1 Hz is obtained. A fractional frequency instability of $2.5\times10^{-16}$ at 1 s is achieved, and reaching $7.5\times10^{-20}$ at 10000 s. The system is stable and able to run for a long time. This work will contribute to optical frequency distribution and remote comparison among atomic clocks.

We present a high power diode-pumped continuous-wave Tm:YLF (Tm$^{3+}$-doped lithium yttrium fluoride) laser with a piece of silicon wafer as the output coupler (Si-OC laser) directly. Under the pump power of 40 W at 793 nm, a maximum output power of 12.1 W is obtained with a beam quality of $M^{2}\le 1.55$ at 1887 nm, corresponding to an optical-to-optical efficiency of 30.25% and a slope efficiency of 33.21%. To the best of our knowledge, this is the first report on directly utilizing silicon as an output coupler (Si-OC) in the solid Tm:YLF laser system. Due to the intriguing characteristics of silicon, such as negligible absorption in the wavelength region around 2 μm, high damage threshold, low cost and long-pass filter properties, double-side polished monocrystalline silicon wafer is considered as an outstanding candidate output coupler in the high-power laser system 2 μm spectral region, which may dramatically reduce the total manufacturing costs of the 2 μm laser system.

A modified Monte Carlo model of speckle tracking of shear wave propagation in scattering media is proposed. The established Monte Carlo model mainly concerns the variations of optical electric field and speckle. The two-dimensional intensity distribution and the time evolution of speckles in different probe locations are obtained. The fluctuation of speckle intensity tracks the acoustic-radiation-force shear wave propagation, and especially the reduction of speckle intensity implies attenuation of shear wave. Then, the shear wave velocity is estimated quantitatively on the basis of the time-to-peak algorithm and linear regression processing. The results reveal that a smaller sampling interval yields higher estimation precision and the shear wave velocity is estimated more efficiently by using speckle intensity difference than by using speckle contrast difference according to the estimation error. Hence, the shear wave velocity is estimated to be 2.25 m/s with relatively high accuracy for the estimation error reaches the minimum (0.071).

In the backward propagation of acoustic waves, the direction of phase velocity is anti-parallel to that of group velocity. We propose a scheme to manipulate the backward propagation using a periodical structure. The dynamic backward propagation process is further experimentally observed. It is demonstrated that the oblique incident plane wave moves backward when it travels through the periodical structure and the backward shift can be controlled within a certain range.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Properties of cylindrical electron acoustic solitons are studied in vortex plasmas. The modified cylindrical Korteweg–de Vries (KdV) equation is acquired and converted into the time fractional cylindrical modified KdV equation by Agrawal's analysis. Via the Adomian decomposition method, a cylindrical soliton solution to the equation is obtained. The cylindrical time fractional effect on the wave properties is investigated. Further, the increase of the fractional order of time $\alpha$ and hot to trapped electrons temperature $\beta$ are minimized in both solitary width and amplitude. These influences on the structures of the soliton may be an alternative to the use of higher order perturbation analysis.

Since runaway electrons and magnetohydrodynamics activity can contribute to serious damage and energy losses in tokamaks, the effect of an external electric field on runaway electrons and hard x-ray spectra is investigated. Parameters such as the plasma current, the hard x-ray photons count and the mean energy of runaway electrons are measured. Positive and negative voltages of 300 V are applied at 10 ms after the plasma initiation (while the plasma is forming), at 15 ms (while the plasma is stable) and at 20 ms (while the plasma is fading away) to attain the most effective time of applying the external electric field. The number of hard x-ray photons has the most changes in the range of 0–200 keV when the external electric fields are applied. Also in the duration of 20–30 ms of plasma the greatest number of hard x-ray spectra is detected. When the external electric fields are applied, the mean energy of runaway electrons reduces significantly, especially at 15 ms (while the plasma is stable).

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy island is used as the start. While the graphene island is removed by oxygenation, the variations of the Rh vacancy island are imaged with an in-situ high-temperature STM. By fitting with our model and calculations, we conclude that the best fit is obtained for 0% Rh, i.e., for the complete absence of nails below graphene on Rh(111). That is, when graphene is formed on Rh(111), the substrate remains flat and does not develop a supporting nail structure.

Two quinary high-entropy alloys (HEAs) with equiatomic concentrations formed by doping either Cu or Al elements into the quaternary NiFeCoCr alloy are produced by arc melting and spray casting techniques. Their entropy of fusion, thermal expansion coefficient and thermal diffusivity are experimentally investigated with differential scanning calorimetry, dilatometry and laser flash methods. The NiFeCoCrCu HEAs contain a face-centered cubic high-entropy phase plus a minor interdendritic (Cu) phase and display a lower entropy of fusion and the Vickers hardness. The NiFeCoCrAl HEAs consist of two body-centered cubic high-entropy phases with coarse dendritic structures and show higher entropy of fusion and the Vickers hardness. Both the thermal expansion coefficient and the thermal diffusivity of the former Cu-doped alloy are significantly larger than those of the latter Al-doped alloy. Although the temperature dependence of thermal diffusivity is similar for both HEAs, it is peculiar that the thermal expansion curve of the NiFeCoCrAl alloy exhibits an inflexion at temperatures of 860–912 K.

Ventilated cavitation plays an important role on the drag reduction of underwater vehicles and surface ships. For the modelling of ventilated cavitation, the minimum speed of the pressure wave is a crucial parameter for the closure of the pressure-density coupling relationship. In this study, the minimum wave speed is determined based on a theoretical model coupling the wave equation and the bubble interface motion equation. The influences of several paramount parameters (e.g., frequency, bubble radius and void fraction) on the minimum wave speed are quantitatively demonstrated and discussed. Compared with the minimum wave speed in the traditional cavitation, values for the ventilated cavitation are much higher. The physical mechanisms for the above difference are briefly discussed with the suggestions on the usage of the present findings.

We report direct nanoscale imaging of ultrafast plasmon in a gold dolmen nanostructure excited with the 7 fs laser pulses by combining the interferometric time-resolved technology with the three-photon photoemission electron microscopy (PEEM). The interferometric time-resolved traces show that the plasmon mode beating pattern appears at the ends of the dimer slabs in the dolmen nanostructure as a result of coherent superposition of multiple localized surface plasmon modes induced by broad bandwidth of the ultrafast laser pulses. The PEEM measurement further discloses that in-phase of the oscillation field of two neighbor defects are surprisingly observed, which is attributed to the plasmon coupling between them. Furthermore, the control of the temporal delay between the pump and probe laser pluses could be utilized for manipulation of the near-field distribution. These findings deepen our understanding of ultrafast plasmon dynamics in a complex nanosystem.

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

Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non-equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of the dot level. The current's strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads. We find that the associated heat by this spin-polarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon. It is also found that both the strength and the resonant peaks' position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads, and then provides an effective method to generate large spin-polarized current with weak heat. Such a result may be useful in designing low energy consumption spintronic devices.

The transport mechanisms of the reverse leakage current in the UV light-emitting diodes (380 nm) are investigated by the temperature-dependent current-voltage measurement first. Three possible transport mechanisms, the space-limited-charge conduction, the variable-range hopping and the Poole–Frenkel emission, are proposed to explain the transport process of the reverse leakage current above 295 K, respectively. With the in-depth investigation, the former two transport mechanisms are excluded. It is found that the experimental data agree well with the Poole–Frenkel emission model. Furthermore, the activation energies of the traps that cause the reverse leakage current are extracted, which are 0.05 eV, 0.09 eV, and 0.11 eV, respectively. This indicates that at least three types of trap states are located below the bottom of the conduction band in the depletion region of the UV LEDs.

The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes (LEDs) is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law $L\propto I^{m}$, with smaller parameter $m$ in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg-defect-related nonradiative centers in the active region. Furthermore, the forward current–voltage characteristics are improved.

AlGaN/GaN high electron mobility transistors (HEMTs) grown on Fe-modulation-doped (MD) and unintentionally doped (UID) GaN buffer layers are investigated and compared. Highly resistive GaN buffers (10$^{9}$ $\Omega$$\cdot$cm) are induced by individual mechanisms for the electron traps' formation: the Fe MD buffer (sample A) and the UID buffer with high density of edge-type dislocations ($7.24\times10^{9}$ cm$^{-2}$, sample B). The 300 K Hall test indicates that the mobility of sample A with Fe doping (2503 cm$^{2}$V$^{-1}$s$^{-1}$) is much higher than sample B (1926 cm$^{2}$V$^{-1}$s$^{-1})$ due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed $I$–$V$ measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage ($-$2.63 V) compared with device B ($-$3.71 V). Lower gate leakage current $|I_{\rm GS}|$ of device A ($3.32\times10^{-7}$ A) is present compared with that of device B ($8.29\times10^{-7}$ A). When the off-state quiescent points $Q_{2}$ ($V_{\rm GQ2}=-8$ V, $V_{\rm DQ2}=0$ V) are on, $V_{\rm th}$ hardly shifts for device A while device B shows +0.21 V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed $I$–$V$ and transconductance $G_{\rm m}$–$V_{\rm GS}$ measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress.

Ni$_{0.7}$Zn$_{0.3}$Fe$_{2}$O$_{4}$/Co$_{0.8}$Fe$_{2.2}$O$_{4}$ (NZFO/CFO) multilayer films are fabricated on Si(100) substrates by the chemical solution deposition method. The microstructure and magnetic properties are systematically investigated. The results of field-emission scanning electronic microscopy show that the grain size of the NZFO/CFO multilayer film is quite uniform and the thickness is about 300 nm. The remanence enhancement effect of the NZFO/CFO multilayer film can be mainly attributed to the exchange coupling interaction between NZFO and CFO ferrite films, which is in favor of the design and fabrication of modern electronic devices.

We investigate numerically the integer quantum Hall effect in a two-orbital square lattice. The Hall plateau $\sigma _{\rm H}=2(e^2/h)$ is well defined with the Chern number $C=\pm 2$. With the increasing disorder, both the Hall plateau and the gap of density of states decrease gradually in width, and finally the gap disappears before vanishing of the Hall plateau. Compared with the Hall plateau induced by the external magnetic field, the one in our system is more robust against disorder. We also find that the transition from the Hall plateau to zero Hall conductance becomes sharper by increasing the size of the system.

We consider a superconducting (Josephson) junction driven by the thermal noise with an ac drive current and a dc constant bias current in the overdamped case and in the underdamped case, respectively, and investigate the effect of the constant bias current on the evolution of the net voltage versus the driving frequency. It is shown that, with some suitably selected values of the system's parameters, suitably increasing the absolute value of the constant bias current can lead to the enhancement of resonant activation of the net voltage versus the driving frequency. This result can benefit the investigation for the Josephson junction subjected to the constant bias current (or voltage).

We investigate the effects of different contents of multiwall carbon nanotubes (MWCNTs) on optical and electrical properties of polyaniline (PANI). The MWCNTs/PANI composites are deposited on glass substrates coated with indium tin oxide (ITO) by the spin-coating technique. The scanning electron microscopy shows that nanotubes are coated with the PANI layer and x-ray diffraction patterns show that all deposited composite films have an amorphous character. The analysis of a UV-vis spectrophotometer indicates the blue shift of the absorbance peak and a decrease in optical band gap value by the enhancement of the CNT content in the PANI matrix while the Urbach energy increases. The Raman spectrum shows the blue shift 1404$\rightarrow$1417 cm$^{-1}$ and photoluminescence spectra show an increase in the intensity of characteristic PANI peak at 436 nm with the increasing CNT content.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Chemically robust conductive p-type boron-doped diamond (BDD) films are an important electrode material and have been widely applied in electrochemistry. In this study, BDD films are taken as a two-dimensional (2D) electrode in a electrophoresis tank system instead of the conventional one-dimensional platinum wire electrode. The theoretical simulations by finite element numerical analysis reveal that the 2D BDD electrodes have relatively high intensity and uniformity of electric field in the tank. Experimentally, the 2D BDD electrodes with smaller size show excellent properties for the separation of DNA fragments. The advantages of the 2D BDD electrodes with chemical inertness, sustainability, high intensity and uniformity electronic field, as well as reduced small size of electrophoresis tank would open a possibility for realizing new generation, high-performance biological devices.

To study the influence of CoFeB/MgO interface on tunneling magnetoresistance (TMR), different structures of magnetic tunnel junctions (MTJs) are successfully prepared by the magnetron sputtering technique and characterized by atomic force microscopy, a physical property measurement system, x-ray photoelectron spectroscopy, and transmission electron microscopy. The experimental results show that TMR of the CoFeB/Mg/MgO/CoFeB structure is evidently improved in comparison with the CoFeB/MgO/CoFeB structure because the inserted Mg layer prevents Fe-oxide formation at the CoFeB/MgO interface, which occurs in CoFeB/MgO/CoFeB MTJs. The inherent properties of the CoFeB/MgO/CoFeB, CoFeB/Fe-oxide/MgO/CoFeB and CoFeB/Mg/MgO/CoFeB MTJs are simulated by using the theories of density functions and non-equilibrium Green functions. The simulated results demonstrate that TMR of CoFeB/Fe-oxide/MgO/CoFeB MTJs is severely decreased and is only half the value of the CoFeB/Mg/MgO/CoFeB MTJs. Based on the experimental results and theoretical analysis, it is believed that in CoFeB/MgO/CoFeB MTJs, the interface oxidation of the CoFeB layer is the main reason to cause a remarkable reduction of TMR, and the inserted Mg layer may play an important role in protecting Fe atoms from oxidation, and then increasing TMR.

Strained-Si$_{0.73}$Ge$_{0.27}$ channels are successfully integrated with high-$\kappa $/metal gates in p-type metal-oxide- semiconductor field effect transistors (pMOSFETs) using the replacement post-gate process. A silicon cap and oxide inter layers are inserted between Si$_{0.73}$Ge$_{0.27}$ and high-$\kappa$ dielectric to improve the interface. The fabricated Si$_{0.73}$Ge$_{0.27}$ pMOSFETs with gate length of 30 nm exhibit good performance with high drive current ($\sim$428 $\mu$A/μm at $V_{\rm DD}=1$ V) and suppressed short-channel effects (DIBL$\sim $77 mV/V and SS$\sim$90 mV/decade). It is found that the enhancement of effective hole mobility is up to 200% in long-gate-length Si$_{0.73}$Ge$_{0.27}$-channel pMOSFETs compared with the corresponding silicon transistors. The improvement of device performance is reduced due to strain relaxation as the gate length decreases, while 26% increase of the drive current is still obtained for 30-nm-gate-length Si$_{0.73}$Ge$_{0.27}$ devices.