International Journal of Modern Physics B

The large nonlinear Hall effect was found in (FeCo)${}_{0.67}$Ge${}_{0.33}$/Ge heterojunctions formed by sputtering amorphous $p$-type (FeCo)${}_{0.67}$Ge${}_{0.33}$ magnetic semiconductor films on near intrinsic n-type Ge substrate. It is very interesting that the mechanisms of the large nonlinear Hall effect in (FeCo)${}_{0.67}$Ge${}_{0.33}$/Ge heterojunctions are different at different temperature ranges. Below 10 K, the Hall resistance of (FeCo)${}_{0.67}$Ge${}_{0.33}$/Ge heterojunctions is almost the same as the anomalous Hall effect of (FeCo)${}_{0.67}$Ge${}_{0.33}$ ferromagnetic films. While the temperature increased from 10 to 60 K, the nonlinear Hall resistance, longitudinal conductance, and magnetoresistance all increased quickly and reached the maximum at T=60 K. In this case, thermally excited conducting carriers can tunnel through the interfacial potential barrier in (FeCo)${}_{0.67}$Ge${}_{0.33}$/Ge heterojunctions. Thus, in the range of 10–60 K, the enhanced nonlinear Hall resistance can be attributed to the anomalous Hall effect which was further enhanced by interfacial Rashba spin–orbit coupling effect. When the temperature further increased from 60 to 250 K, the interfacial potential barrier weakened gradually, and the Hall resistance and magnetoresistance decreased due to the shunting of the Ge substrate. In this case, the nonlinear Hall effect of (FeCo)${}_{0.67}$Ge${}_{0.33}$/Ge heterojunctions can be explained very well by the two-band model of nonlinear Hall effect.

By numerically solving the time-dependent Schrödinger equation for helium atoms in a single mid-infrared laser field, we explore the frequency-chirping effect of laser field on high-order harmonic and isolated attosecond pulse generation. One or two ultrabroad supercontinuum harmonic plateaus can be controlled through modulating the laser field frequency by a small time-dependent signal. Under the best chirping condition, an ultrashort 2.2 as pulse can be obtained by Fourier transformation with the bandwidth of 782 eV. Furthermore, we explain the harmonic generation physical mechanisms by classical ionizing and returning energy maps and time–frequency analyzes.

To make an insight into the interaction characteristics of a flat plate rotating in laminar flows, the immersed boundary (IB)-lattice Boltzmann (LB) method combined with the multiple-relaxation-time (MRT) collision model in two dimensions is presented. Furthermore, an implicit velocity-correction IB method is proposed to deal with the interface of moving solid boundary interacting with fluid flows. Two valuable sub-issues are particularly highlighted in the research. One is the multiple-relaxation-time immersed boundary-lattice Boltzmann (MRT-IB-LB) implementation of the fluid-structure interface enforcing the nonslip boundary condition, and the other is the effects of rotating velocities associated with aspect ratios on the plate interacting with the flows. The model is validated with the benchmark case: the flow around a cylinder asymmetrically placed in a channel. Then the effects of different rotating velocities and aspect ratios are researched. With the increasing of aspect ratios, the vortex shedding frequency increases and the multiple dominant frequencies of the hydrodynamic force occur. The formed vortices are driven downstream and amalgamated into the dominant vortices in the biased flow. The average values of hydrodynamic forces can be enlarged by increasing aspect ratio. Additionally, the drag coefficient can be decreased but the lift coefficient is increased by increasing the rotating velocity.

A new zigzag lattice phononic crystal with holes is designed. Nondominated sorting genetic algorithm-II (NSGA-II) is used for the optimization of the newly designed phononic crystal (PC). Results indicate that geometrical parameters are key factors as well as density and elastic modulus for the determination of the bandgaps (BGs). The width of the BG of the optimized PC with holes can be increased three times higher than the initial design without holes.

Molecular dynamics (MD) simulations have been employed to simulate the structure of Ni nanoparticles (NPs). These NPs consist of 500, 1372, 2916 and 5324 atoms. Various structures of these NPs, consisting of faced-centered cubic (fcc), hexagonal closed packed (hcp), icosahedral (ico) and amorphous states, have been simulated by changing the cooling rate from 2000 to 300 K. The models of mixed core/shell spin (1, 3/2) have been set based on the NPs. Monte Carlo (MC) simulation has been applied to investigate the magnetic behavior and phase diagrams of the models. We have found that the structure of the models plays important role on the characteristic phase diagrams. The effects of the atomic number as well as the exchange coupling J${}_{\mathrm{\text{sh}}}$/J${}_{\mathrm{\text{c}}}$ (J${}_{\mathrm{\text{sh}}}$ — the shell coupling and J${}_{\mathrm{\text{c}}}$ — the core coupling) on the thermal and magnetic behaviors of the models have been presented and discussed. The phase diagrams in k${}_{\mathrm{\text{B}}}$T/J${}_{\mathrm{\text{c}}}$−J${}_{\mathrm{\text{sh}}}$/J${}_{\mathrm{\text{c}}}$ plane also have been observed by changing the structure and the number atoms of the models.

The aim of the present study is to investigate the effect of the counter-rotating terms on the quantum dynamics of a harmonic oscillator in the presence of a deformed bath. We first obtain the Langevin equation of motion for damped oscillator with and without the rotating-wave approximation (RWA). Then, we study the effect of the counter-rotating terms on the diffusion coefficients. Then, we obtain the equation of motion for the harmonic oscillator correlation function with and without the RWA. Finally, we investigate the influence of the counter-rotating terms on the oscillator correlation function.

In this paper, the effect of different hopping rates coupled with on-ramp on the phase diagrams has been investigated by totally asymmetric simple exclusion process (TASEP). The topology of phase diagrams on different hopping rates and on-ramp has been obtained. Additionally, the corresponding phase diagrams and the existing condition are given by approximate mean field theory, and the theoretical results agree well with Monte Carlo simulations.

We report a comparative study of scattering rates which are calculated using different formalisms such as [P. B. Allen, Phys. Rev. B 3, 305 (1971); S. V. Shulga, D. V. Dolgov and E. G. Maksimov, Physica C 178, 266 (1991); B. Mitrović and M. A. Fiorucci, Phys. Rev. B 31, 2694 (1985); S. G. Sharapov and J. P. Carbotte, Phys. Rev. B 72, 134506 (2005)] and memory function formalism (MemF) [H. Mori, Prog. Theor. Phys. 33, 423 (1965)]. An advantage of this study is that it sheds light on the physical assumptions used in these formalisms. In this context, we consider a case of electron–phonon interaction and discuss frequency- and temperature-dependent behavior of scattering rates. Further, a comparative study of scattering rate proceeds for distinct phonon density of states (PDOS) and electron density of states (EDOS). From the detailed analysis, we observe that the MemF is the most general one and others are based on restrictive assumptions as discussed in this work.

In statistical physics, researchers concentrate on mass diffusion and heat conduction-based information filtering models, which effectively facilitate recommendation accuracy and diversity. There are many improved methods combining mass diffusion with heat conduction theories. Research results show that the best results are achieved when the combination of mass diffusion and heat conduction reaches equilibrium. With elaborative analysis, we find that similarity redundancies derive from the attribute correlations of objects, and deduce the similarity estimation deviation. Considering the former deficiencies, we propose a novel model through eliminating redundant diffusion and compensating balance (shortly ERD-CB), which symmetrically combines mass diffusion with heat conduction process through balance compensation. Three benchmark datasets from Movielens, Amazon and Netflix are used in our extensive experiments. Experiment results show that the ERD-CB model outperforms the benchmarkbaselines for accuracy, diversity and novelty.

The waveform control in the improvements of high-order harmonic generation (HHG) spectra and attosecond pulse signals driven by the two-color and three-color combined fields has been theoretically investigated. (a) The results show that by properly controlling the $\omega$–2$\omega$ two-color laser beam (including the modulations of chirps, carrier envelope phases and delay time), either the harmonic cutoff can be extended, showing a water window spectral continuum, or the selective enhancement of the single-order and two-order harmonics can be found. Further, with the introduction of a third controlling field, the efficiency of spectral continuum can be enhanced by two orders of magnitude compared with that from the two-color field. Moreover, the enhancement of HHG is not very sensitive to the frequency of the third field (i.e., the frequency of the third field is chosen to be 3$\omega$, 4$\omega$ and 6$\omega$). Thus, some water window attosecond pulses with the durations of 60 as can be obtained. (b) Furthermore, the harmonic cutoff can be further extended when using a half-cycle controlling pulse or introducing the inhomogeneous effect of the laser field. Moreover, the efficiency of HHG can be further improved when the initial state is prepared as the superposition state of the ground state and some excited state of He atom. Consequently, a much broader spectral continuum with an intensity enhancement of another two orders of magnitude can be found. Finally, through the Fourier transformation of some spectral continuum, the intense water window attosecond pulses with the durations of 60 as can be produced.

Within the framework of the effective-mass approximation and by using a variational and perturbation approach, the binding energies and photoionization cross-sections of donor and acceptor impurities in an inverted core/shell ellipsoidal spherical quantum dot under an applied magnetic field have been studied. We have calculated the binding energies of both donor and acceptor impurities as a function of the core and shell sizes and shapes with different impurity positions under the applied magnetic field. In addition, the corresponding photoionization cross-section is calculated. Our results show that the binding energy of the acceptor impurity is larger than that of the donor impurity, and both of them with different impurity positions and quantum ellipsoid anisotropies will exhibit a nonmonotonic change. The peak value of the photoionization cross-section will reach a maximum with the increasing ratio R₁/R₂. It is found that the applied magnetic field can be an effective means of enhancing the photoionization cross-section of an impurity state in such core/shell quantum dot system.

For the limitation that current node influence ranking algorithms can only be applied in a single type of network and the results are inaccurate, an algorithm based on similarity is proposed. When a node is similar to many nodes in the network, it is representative and can be treated as an influential node. Firstly, probability walking model is used to simulate the initiative visit between nodes in different types of networks. Secondly, superposed probabilistic transfer similarity is defined based on the model considering nodes’ inbound and outbound information. Finally, node ranking algorithm is set up using the new similarity measuring method. Experiments show that the algorithm can evaluate different kinds of networks with high accuracy, whether the network is directed or undirected, weighted or unweighted.

Detecting the natural communities in a real-world network can uncover its underlying structure and potential function. In this paper, a novel community algorithm SUM is introduced. The fundamental idea of SUM is that a node with relatively low degree stays faithful to its community, because it only has links with nodes in one community, while a node with relatively high degree not only has links with nodes within but also outside its community, and this may cause confusion when detecting communities. Based on this idea, SUM detects communities by suspecting the links of the maximum degree nodes to their neighbors within a community, and relying mainly on the nodes with relatively low degree simultaneously. SUM elegantly defines a similarity which takes into account both the commonality and the rejective degree of two adjacent nodes. After putting similar nodes into one community, SUM generates initial communities by reassigning the maximum degree nodes. Next, SUM assigns nodes without labels to the initial communities, and adjusts the border node to its most linked community. To evaluate the effectiveness of SUM, SUM is compared with seven baselines, including four classical and three state-of-the-art methods on a wide range of complex networks. On the small size networks with ground-truth community structures, results are visually demonstrated, as well as quantitatively measured with ARI, NMI and Modularity. On the relatively large size networks without ground-truth community structures, the performances of these algorithms are evaluated according to Modularity. Experimental results indicate that SUM can effectively determine community structures on small or relatively large size networks with high quality, and also outperforms the compared state-of-the-art methods.

Y-type hexagonal ferrite (CaBaCo₂Ga${}_{0.5}$Fe${}_{11.5}$O${}_{22}$) was synthesized by sol–gel technique. The ferrite–polymer composites (1−x)CaBaCo₂Ga${}_{0.5}$Fe${}_{11.5}$O${}_{22}$+(x)polyaniline (x=0.25, 0.50, 0.75, 1) namely PF1, PF2, PF3 and polyaniline (PANI) were synthesized by in situ polymerization. The synthesized samples were characterized by XRD, SEM, electrical and dielectric measurements, optical and magnetic studies. XRD pattern reveals a broad peak of polyaniline which is an indication of amorphous nature of PANI. Room-temperature resistivity increases from 2.14 × 10¹ $\mathrm{\Omega }\cdot$cm to 2.78 × 10${}^{10}\mathrm{\Omega }\cdot$cm as ferrite content increases due to resistive behavior of the ferrite particles dispersed in the PANI matrix. The value of dielectric constant decreases at fixed frequency with increasing concentration of ferrite filler which is predominantly due to exchange of electrons between Fe${}^{+2}$ and Fe${}^{+3}$ ions that ultimately results in enhancement of electric polarization and conductivity. The optical bandgap increases with increasing amount of ferrite in the composites. The saturation magnetization and remanence increase with the increase of ferrite filler amount in PANI matrix whereas coercivity decreases. The decrease in coercivity and increase in saturation magnetization are related to Brown’s relation. The present nanocomposite samples may be the best candidates for electromagnetic shielding.