We investigate theoretically the Landau levels (LLs) and magneto-transport properties of phosphorene under a perpendicular magnetic field within the framework of the effective k·p Hamiltonian and tight-binding (TB) model. At low field regime, we find that the LLs linearly depend both on the LL index n and magnetic field B, which is similar with that of conventional semiconductor two-dimensional electron gas. The Landau splittings of conduction and valence band are different and the wavefunctions corresponding to the LLs are strongly anisotropic due to the different anisotropic effective masses. An analytical expression for the LLs in low energy regime is obtained via solving the decoupled Hamiltonian, which agrees well with the numerical calculations. At high magnetic regime, a self-similar Hofstadter butterfly (HB) spectrum is obtained by using the TB model. The HB spectrum is consistent with the LL fan calculated from the effective k·p theory in a wide regime of magnetic fields. We find the LLs of phosphorene nanoribbon depend strongly on the ribbon orientation due to the anisotropic hopping parameters. The Hall and the longitudinal conductances (resistances) clearly reveal the structure of LLs.

Using the non-equilibrium Green function method, we study the Andreev reflection in a Y-shaped graphene-superconductor device by tight-binding model. Considering both the zigzag and armchair terminals, we confirm that the zigzag terminals are the better choice for detecting the Andreev reflection without no external field. Due to scattering from the boundaries of the finite-size centre region, the difference between Andreev retroreflection and specular reflection is hard to be distinguished. Although adjusting the size of the device makes the difference visible, to distinguish them quantitatively is still impossible through the transport conductance. The problem is circumvented when applying a perpendicular magnetic field on the centre region, which makes the incident electrons and the reflected holes propagate along the edge or the interface. In this case, the retroreflected and specular reflected holes from the different bands have opposite effective masses, therefore the moving direction of one is opposite to the other. Which external terminal the reflected holes flow into depends entirely on the kind of the Andreev reflection. Therefore, the specular Andreev reflection can be clearly distinguished from the retroreflected one in the presence of strong magnetic field, even for the device with finite size.

In the paper, a cross chaotic map using Logistic map and Chebyshev map is presented. With the exceptionally desirable properties of non-periodical motion and non-convergence of chaos, scheme for image encryption has suggested a new and efficient way to deal with the intractable problem of fast and highly secure image. In order to realize image encryption, every pixel of image is randomly changed according to encryption matrix in the process of grayscale substitution; simultaneously scrambling transformation technique (row rotation and column rotation technique) is used in the process of position permutation. The experimental results indicate the scheme is more secure and efficient than conventional ones, and it is feasible.

We study the effect of impurity scattering effect in black phosphorurene (BP) in this work. For single impurity, we calculate impurity induced local density of states (LDOS) in momentum space numerically based on tight-binding Hamiltonian. In real space, we calculate LDOS and Friedel oscillation analytically. LDOS shows strong anisotropy in BP. Many impurities in BP are investigated using T -matrix approximation when the density is low. Midgap states appear in band gap with peaks in DOS. The peaks of midgap states are dependent on impurity potential. For finite positive potential, the impurity tends to bind negative charge carriers and vise versa. The infinite impurity potential problem is related to chiral symmetry in BP.

In this study, we show that the local Andreev reflection not only can be tuned largely by the type of the normal metal electrode, it also is related to the electrostatic potential in the superconductor region in a MoS 2 -based n(p)-type metal/superconductor junction. In a MoS 2 -based n-type metal/n(p)-type superconductor/p-type metal (nSp) transistor, nonlocal pure valley-and spin-entangled current can be tuned by the length and local gate voltage of a superconductor region. In particular, switching the quasiparticle type in both structures results in a series of intriguing features. Such an effect is not attainable in a graphene-based junction where the electron-hole symmetry enables the symmetry results to be observed. Besides, we have shown that the crossed Andreev reflection exhibits a maximum around ξ/2 instead of the exponential decay behavior in conventional superconductors and a maximum around ξ in the graphene material. The proposed straightforward experimental design and pure valley-and spin-entangled state can pave the way for a wider use in the entanglement based on material group-VI dichalcogenides.

To our knowledge, this paper investigates the first application of meta-heuristic algorithms to tackle the parallel machines scheduling problem with weighted late work criterion and common due date (). Late work criterion is one of the performance measures of scheduling problems which considers the length of late parts of particular jobs when evaluating the quality of scheduling. Since this problem is known to be NP-hard, three meta-heuristic algorithms, namely ant colony system, genetic algorithm, and simulated annealing are designed and implemented, respectively. We also propose a novel algorithm named LDF (largest density first) which is improved from LPT (longest processing time first). The computational experiments compared these meta-heuristic algorithms with LDF, LPT and LS (list scheduling), and the experimental results show that SA performs the best in most cases. However, LDF is better than SA in some conditions, moreover, the running time of LDF is much shorter than SA.

Because of the helicity of electrons in HgTe quantum wells (QWs) with inverted band structures, the electrons cannot be confined by electric barriers since electrons can tunnel the barriers perfectly without backscattering in the HgTe QWs. This behavior is similar to Dirac electrons in graphene. In this paper, we propose a scheme to confine carriers in HgTe QWs using an electric-magnetic barrier. We calculate the transmission of carriers in 2-dimensional HgTe QWs and find that the wave-vector filtering effect of local magnetic fields can confine the carriers. The confining effect will have a potential application in nanodevices based on HgTe QWs.

Based on the Born-Oppemheimer approximation, we divide the total electron Hamiltonian in a spin-orbit coupled system into the slow orbital motion and the fast interband transition processes. We find that the fast motion induces a gauge field on the slow orbital motion, perpendicular to the electron momentum, inducing a topological phase. From this general designing principle, we present a theory for generating artificial gauge field and topological phase in a conventional two-dimensional electron gas embedded in parabolically graded GaAs/InxGa1−xAs/GaAs quantum wells with antidot lattices. By tuning the etching depth and period of the antidot lattices, the band folding caused by the antidot potential leads to the formation of minibands and band inversions between neighboring subbands. The intersubband spin-orbit interaction opens considerably large nontrivial minigaps and leads to many pairs of helical edge states in these gaps.