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We propose a possible spatial spin filter on a Y-shaped zigzag silicene nanoribbon (ZSNR) junction with different even(odd)-chain electrodes by applying three pumping electric fields. By means of the tight-binding model and Keldysh Green's function method, we calculate the spin-dependent tunneling currents on the middle–left (M–L) and middle–right (M–R) terminals of Y-shaped ZSNR junction, and find that this spin pump not only can generate a pure spin current and a 100% polarized spin current at a zero bias, but also can spatially separate spin up and spin down currents on its even(odd)-chain M–L(R) terminals. The spatial spin filtering phenomena might come from the combination of the even–odd chain effect and single photon-assisted pumping process. The pumped spin up(down) current and its ON(OFF) transport states on M–L(R) terminal of the Y-shaped ZSNR junction can be modulated by almost all the device's parameters such as the Fermi level, pumping frequency, spin–orbit coupling, staggered lattice potential and magnetization distribution. We also explore the possible way to close the spatial spin filtering behaviors in the device. Our findings might be useful for producing and separating 100% polarized spin up and down currents on multi-terminal silicene nanodevices. [ABSTRACT FROM AUTHOR]

We derive an analytical model for calculating the optical activity in monolayer black phosphorus under an external magnetic field. By optimizing the parameters, the circular dichroism can be comparable to that in previously reported chiral metamaterials in a broad angle range. Besides, the optical activity including the circular dichroism, the circular conversion dichroism and the circular birefringence can be tuned almost linearly via changing the applied magnetic field magnitude. These results show that our proposed model would possess potential applications in polarization optics, stereochemistry, and molecular biology. [ABSTRACT FROM AUTHOR]

We address the issue of dissipative vs. non-dissipative behavior in a mesoscopic set of coupled elements such as oscillators, with one half having gain and the other half having losses. We introduce a graph with coupling as the graph edges in given fixed number and gain/loss elements as its nodes. This relates to parity-time symmetry, notably in optics, e.g. set of coupled fibers, and more generally to the issue of taming divergence related to imaginary parts of eigenvectors in various network descriptions, for instance biochemical, neuronal, ecological. We thus look for the minimization of the imaginary part of all eigenvalues altogether, with a collective figure of merit. As more edges than gain/loss pairs are introduced, the unbroken cases , i.e., stable cases with real eigenvalues in spite of gain and loss, become statistically very scarce. A minimization from a random starting point by moving one edge at a time is studied, amounting to investigate how the hugely growing configuration number impedes the attainment of the desired minimally-dissipative target. The minimization path and its apparent stalling point are analyzed in terms of network connectivity metrics. We expand in the end on the relevance in biochemical signaling networks and the so-called "stability-optimized circuits" relevant to neural organization. [ABSTRACT FROM AUTHOR]

Utilizing first-principles calculations, we have investigated the structural, electronic, and optic properties of a series of two-dimensional (2D) stable direct band-gap semiconductors, which are M2XY (M = Ga, In; X,Y = S, Se, Te) in group-III-V with the Janus single layer structures. Meanwhile, the MX (M = Ga, In; X = S, Se, Te) of binary single layer structures, which are parent materials for Janus structures, have also been investigated. The electronic structures are calculated via GW0 self-consistency, and the results show that these Janus monolayer structures belong to the direct band-gap semiconductors with large band gap. In contrast to the indirect band-gap MX monolayers, it indicates that an indirect-direct band-gap transition can be realized by constructing Janus structures. Moreover, we systematically investigated the optic response properties of M2XY Janus single layers by solving the Bethe-Salpeter equation (BSE), and the exciton absorption peaks are observed in these monolayer structures. Our results show that these Janus structure materials should be potential candidates for optoelectronic nanodevices. [ABSTRACT FROM AUTHOR]

Intriguing issues in one-dimensional non-reciprocal topological systems include the breakdown of usual bulk-edge correspondence and the occurrence of half-integer topological invariants. In order to understand these unusual topological properties, we investigate the topological phase diagrams and the zero-mode edge states of a generalized non-reciprocal Su-Schrieffer-Heeger model with a general form fulfilling the chiral symmetry, based on some analytical results. Meanwhile, we provide a concise geometrical interpretation of the bulk topological invariants in terms of two independent winding numbers and also give an alternative interpretation related to the linking properties of curves in three-dimensional space. For the system under the open boundary condition, we construct analytically the wavefunctions of zero-mode edge states by properly considering a hidden symmetry of the system and the normalization condition with the use of biorthogonal eigenvectors. Our analytical results directly give the phase boundary for the existence of zero-mode edge states and unveil clearly the evolution behavior of edge states. In comparison with results via exact diagonalization of finite-size systems, we find our analytical results agree with the numerical results very well. [ABSTRACT FROM AUTHOR]

In this work, we first use the finite-differential time-domain (FDTD) to calculate the eigenenergies and eigenfunctions of a three dimensional (3D) cylindrical quantum wire. We assume that the inside of the wire is at zero potential. But, the outside of the wire has been chosen at different potentials as infinite and finite values. This is a true 3D procedure based on a direct implementation of the time-dependent Schrödinger equation. Then, we apply the Shannon and Tsallis entropy to obtain entropy and specific of the system. The results show that (i) the specific heat obtained by Tsallis has a peak structure. (ii) The entropy behavior for the finite and infinite confining potential has the same behavior at low temperatures. (iii) The peak value of specific heat increases with enhancing the quantum wire radius. [ABSTRACT FROM AUTHOR]

We revisit the classical problem of electromagnetic wave refraction from a lossless dielectric to a lossy conductor, where both media are considered to be non-magnetic, linear, isotropic and homogeneous. We derive the Fresnel coefficients of the system and the Poynting vectors at the interface, in order to compute the reflectance and transmittance of the system. We use a particular parametrisation of the referred Fresnel coefficients so as to make a connection with the ones obtained for refraction by an interface between two lossless media. This analysis allows the discussion of an actual application, namely the Fresnel polarisation of infra-red radiation by elemental bismuth, based on the concept of pseudo Brewster's angle. [ABSTRACT FROM AUTHOR]

The problem of exciton states in spherical semiconductor quantum dots is revisited, employing the finite element method to numerically solve the system of differential equations for the center of mass and relative motion of the interacting electron-hole pair. This process is performed within the effective mass and parabolic bands approximations. The use of a finite confinement together with a parabolic description of the conduction and valence band profiles prevents the two equations from uncoupling. The allowed energies are reported as functions of the quantum dot radius. A comparison of theoretically determined fundamental photoluminescence peak energies with available experimental reports in the cases of CdS, CdSe and CdTe is presented and discussed, showing a good agreement between calculated and measured results. [ABSTRACT FROM AUTHOR]

Present study endeavors to analyze the role of Gaussian white noise and fluctuating confinement potential on time-average excitation rate (TAER) of impurity doped quantum dot (QD). The TAER profiles are exhaustively monitored as a number of physical quantities are varied over a range with and without noise. Application of noise to the system takes place in two different pathways known as 'additive' and 'multiplicative'. And the fluctuation of the confinement potential has been considered to be cosinusoidal and random which induces the excitation of ground state electronic population to the higher states. The TAER profiles comprise of features like steady increase/decrease, maximization, minimization and saturation. However, the specific characteristics of a particular profile depend on presence/absence of noise, the noise mode, the nature of fluctuating confinement potential and the identity of the physical quantity being varied. Production of large TAER of doped QD depends on noise-mode and nature of fluctuating confinement potential based on which the noise strength is required to be maintained in the vicinity of some typical values. [ABSTRACT FROM AUTHOR]

Firstly, the multi-band semiconductor Bloch equations (MB-SBE) for the quantum optical properties are reformulated in momentum space to investigate the influence of spin-orbit couplings (SOCs) on the linear optical response of semiconducting carbon nanotubes (SCNTs). One remarkable feature in numerical results is that a new low-strength peak appears at the lower-excited energy position than the peak E11. Comparing the data with/without SOCs, obviously, this new lowest-excited peak originates from the brightened spin-triplet exciton E11T, which has higher binding energy than the spin-singlet exciton E11S. For eight SCNTs with small radius, further comparison shows that the appearance and strength of this new peak E11T is dependent on the chiral of SCNTs. For (n, 1) tubes belonging to the family ν = +1 the effect of SOCs on this new brightened peak E11T is stronger relative to other SCNTs having the approximative strength of SOCs. [ABSTRACT FROM AUTHOR]

Advances in the fabrication and characterization of nanowires polytypes have made crystal phase engineering a well-established tool to tailor material properties. In this review, recent progresses in the field are described, with special focus on the central role that crystal phase has in modulating the electronic and optical properties of nanowires. We start with an overview on III-V nanowires, which have been developed first and for which more experimental results already exist. Then, particular attention will be devoted to group IV polytypes which represent one of the most exciting and novel topic in the field. A survey of both theoretical and experimental efforts will be provided with the final aim of highlighting the importance of crystal phase control in materials design. [ABSTRACT FROM AUTHOR]

Localization phenomena of non-interacting electrons are critically investigated in a quantum network where site energies and/or hopping integrals are correlated in the form of Aubry-André-Harper (AAH) model. In presence of diagonal hopping between neighboring strands of the network an energy zone, consists of extended and localized states, appears whose width can be adjusted by tuning the physical parameters describing the system. It gives an important signature towards the detection of mobility edge which we justify by analyzing the energy band spectra. Finally, we study the interplay between the diagonal and off-diagonal disorders, and explore the robust delocalizing effect. Our analysis may lead to important aspects of electronic localization in coupled AAH chains. [ABSTRACT FROM AUTHOR]

Understanding the origin of photoluminescence intermittency and its correlation with microstructure is crucial for the design and preparation of quantum dots (QDs) with high fluorescence quantum yield. ZnSe clusters provide a typical model for studying the effect of their size, geometrical and electronic structures on their radiative and non-radiative process of II-VI QDs. The rate constants of radiative and non-radiative processes, kr and knr, of the (ZnSe)n clusters were computed by using first-principles calculations, Einstein spontaneous radiation theory and Fermi's golden rule. The kr and knr variations with cluster size were analyzed in term of a number of quantities. Emission energy and reorganization energy were identified to play dominant roles in the determination of kr and knr for the studied clusters. Furthermore, a correlation between these two quantities and the geometric rigidity of the ZnSe clusters was revealed. The clusters with greater geometric rigidity tend to possess larger emission energy, and smaller reorganization energy. While radiative and non-radiative electron–hole recombination rates of the ZnSe clusters vary in a complicated way because of their diverse structures and prominent quantum size effect, our study highlights the correlation between recombination rate and cluster structure, which would be helpful for the design of QD materials with high fluorescence quantum yields. [ABSTRACT FROM AUTHOR]

Optimal population inversion of a single two-level system (TLS) coupled to an Ohmic boson bath via off-diagonal TLS-bath coupling is studied by using optimal control theory. In the weak system-bath coupling regime where the Bloch-Redfield formalism is applicable, we derive the Bloch equation for describing the evolution of the dissipative TLS in the presence of a time-dependent external control field. By using the automatic differentiation technique to compute the gradient for the cost functional, we calculate the optimal energy difference profile that can achieve an ideal inversion. Further we examine the robustness of driving-induced tunneling oscillations (DITO) in presence of dissipation. [ABSTRACT FROM AUTHOR]

In the present work, we have used ab initio molecular dynamics (AIMD) and non-equilibrium Green's function (NEGF) formalism to investigate the scaling behavior of electron transport in ultra-thin films of Ge2Sb2Te5 (GST). The relation between the thickness of GST and its electron transport properties are studied in both crystalline (c-GST) and amorphous (a-GST) phases. For thin films with lower than 36 Å thickness, we have observed a dramatic increase in the conductivity of the amorphous phase and an associated reduction in the conductance contrast between the two phases. Metal-induced gap states (MIGS) near the electrodes are observed in the density of states and the transmission coefficient of a-GST. The disappearance of the bandgap of a-GST due to the overlap of MIGS is responsible for the sharp reduction of crystalline to amorphous conductance ratio (ON/OFF). The ON/OFF ratio of the devices is about one order of magnitude upon downscaling the ultra-thin film of the active bit to 36 Å. This estimation is the ultimate scalability for the simulated PCM device. When the thickness of GST further scales down, the reliable read operation is not possible. Our results show very good agreement with experimental work and it seems promising to engineers and designers of ultra-thin PCM devices. [ABSTRACT FROM AUTHOR]

Rashba and Dresselhaus spin–orbit interactions (SOIs), external fields and dielectric environment effects on hydrogenic impurity states in core–shell (ZnO/ZnS) and inverted core–shell (ZnS/ZnO) quantum dots were studied. We employed the finite difference method to achieve energy eigenvalues of the system. Our results demonstrate that SOIs, external fields and dielectric environment change drastically the impurity states. Besides, the spin degeneracy is removed when both the SOIs and the Zeeman effect are simultaneously considered. [ABSTRACT FROM AUTHOR]

Nanocrystalline NiWO4 powder samples were synthesized by direct-chemical precipitation method. Thermal stability of the sample was studied by thermo gravimetric and differential thermal analysis. Structural characterization of NiWO4 nanoparticles was done with X-ray diffraction and field emission scanning electron microscopy. Elemental analysis of the samples were done with energy dispersive X-ray spectroscopy. Vibration modes of as prepared samples were analysed using Fourier transform infrared spectroscopy and Raman spectroscopy. Optical properties of the samples were explored using UV-vis spectroscopy and photoluminescence (PL) spectroscopy. Magnetic properties of NiWO4 nanoparticles were analysed using vibrating sample magnetometer (VSM). Effect of calcination temperature on structural, vibrational, optical and magnetic properties of the NiWO4 samples were also investigated. The results obtained from various characterization techniques found that NiWO4 nanoparticle have the potential use in light emitting diodes (LEDs), biomedical and sensing applications. [ABSTRACT FROM AUTHOR]

We investigate the neutron polarization induced by interfering pseudospins between two graphene sheets inserted into a cavity with a circularly polarized photon field. We find that only when two graphene sheets are located at the coordinate positions of some antinodes of standing photon field, the neutron polarization is most remarkable. This is caused by an interference effect of pseudospins between two graphene sheets induced by photons and neutron. This neutron polarization mechanism has potential application on neutron polarization device. [ABSTRACT FROM AUTHOR]

The linear response transport properties of carbon nanotube quantum dot in the strongly correlated regime are discussed. The finite-U mean field slave boson approach is used to study many-body effects. Magnetic field can rebuilt Kondo correlations, which are destroyed by the effect of spin-orbit interaction or valley mixing. Apart from the field induced revivals of SU(2) Kondo effects of different types: spin, valley or spin-valley, also more exotic phenomena appear, such as SU(3) Kondo effect. Threefold degeneracy occurs due to the effective intervalley exchange induced by short-range part of Coulomb interaction or due to the intershell mixing. In narrow gap nanotubes the full spin-orbital degeneracy might be recovered in the absence of magnetic field opening the condition for a formation of SU(4) Kondo resonance. [ABSTRACT FROM AUTHOR]

Multi-branched gold nanostars with fractal feature were synthesized using the Triton X-100 participant seed-growth method. By increasing the amount of ascorbic acid, the branch length of gold nanostars could be greatly increased. It has been interesting to find that the secondary growth of new branches takes place from the elementary structure when the aspect ratio of the branches is greater than 8.0 and the corresponding plasmon absorption wavelength is greater than 900 nm. Raman activity of the gold nanostar films has been investigated by using the 4-mercaptobenzoic acid (4-MBA) as Raman active probe. Experimental results show that the surface-enhanced Raman scattering (SERS) ability of the gold nanostars could be efficiently improved when the fractal structure appears. The physical mechanism has been attributed to the intense increased secondary branch number and the increased 'hot spots'. These unique multi-branched gold nanostars with fractal feature and great SERS activity should have great potential in sensing applications. [ABSTRACT FROM AUTHOR]

The energy dissipation and heat flows associated with the particle current in a system with a molecular junction are considered. In this connection, we determine the effective temperature of the molecular oscillator that is compatible with the existence of a steady state. The calculations based on the Kadanoff-Baym nonequilibrium Green function formalism are carried out supposing a strong coupling of the dot electrons with the molecular vibrations. Accordingly, the representation given by the Lang-Firsov polaron transformation is used and the dependence of results on the electron-phonon interaction strength is investigated. [ABSTRACT FROM AUTHOR]

We investigate statistical aspects of the entanglement production for open chaotic mesoscopic billiards in contact with superconducting parts, known as Andreev billiards. The complete distributions of concurrence and entanglement of formation are obtained by using the Altland-Zirnbauer symmetry classes of circular ensembles of scattering matrices, which complements previous studies in chaotic universal billiards belonging to other classes of random matrix theory. Our results show a unique and very peculiar behavior: the realization of entanglement in a Andreev billiard always results in non-separable state, regardless of the time reversal symmetry. The analytical calculations are supported by a numerical Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

We study the Majorana bound states (MBS) arising in finite-size strips with Rashba spin-orbit coupling in the presence of an in-plane Zeeman magnetic field. Using two different methods, first, the numerical diagonalization of the tight-binding Hamiltonian, and second, finding the singular points of the Hamiltonian [I. Mandal, Europhys. Lett. 110, 67005 (2015); I. Mandal, S. Tewari, Physica E 79, 180 (2016); I. Mandal, Condens. Matter Phys. 19, 33703 (2016); P. San-Jose, E. Prada, R. Aguado, Sci. Rep. 6, 21427 (2016)], we obtain the topological phase diagram for these systems as a function of the chemical potential and the magnetic field, and we demonstrate the consistency of these two methods. By introducing disorder into these systems we confirm that the states with even number of Majorana pairs are not topologically protected. Finally, we show that a calculation of the ℤ topological invariants recovers correctly the parity of the number of MBS pairs, and it is thus fully consistent with the phase diagrams of the disordered systems. [ABSTRACT FROM AUTHOR]

In this research, we investigate the influence of the screw dislocation on the energy levels of nonrelativistic electrons on a two-dimensional solid taking into account the deformed Kratzer potential under an external magnetic and the Aharonov-Bohm (AB) fields. We obtain the bound state energy eigenvalues equation and the corresponding wave functions by using the Frobenius method. We also calculate the direct interband light absorption coefficient and threshold frequency of absorption in a quantum pseudodot. Some of the numerical results are given. [ABSTRACT FROM AUTHOR]

For a nonperiodic system, a bamboo SiGe nanowire with axially degraded components, it is impossible to obtain its phonon dispersion relations through lattice dynamic or the first principle calculation. Therefore, we present a simple and available method to solve this problem. At first, the SiGe nanowire with axially degraded component is divided into several sections according to its component distribution like bamboos' sections formed in the growth process. For each section with a given x value, we constructed a pseudo-cell to calculate its phonon dispersion relations. Thermal conductances of junctions and of each section are then calculated by the phonon mismatch model and the phonon transmission probability with diffusive and ballistic portions. The dependences of thermal conductivity on the length of each section and the gradient of degraded component between sections are presented. We studied thermal conductivity dependence on temperature, length and diameter of the SiGe nanowire with axially degraded component. And we found κ ~ l , in which the exponent 0.8 is ascribed to the competition between phonons ballistic and diffusive transport. Furthermore, thermal conductivities along axial (100), (110), and (111) directions are discussed in detail. The method provides a simple and available tool to study thermal conductivity of a non-period system, such as a quasiperiodic superlattice or a nanowire with axially degraded component. [ABSTRACT FROM AUTHOR]

Indirect exchange interaction between two magnetic external atoms, named by Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction, has been presented in the staggered armchair graphene nanoribbon. We have studied RKKY interaction as a function of distance between localized moments. It has been shown that a magnetic ordering along the z-axis mediates an anisotropic interaction which corresponds to a XXZ model interaction between two magnetic moments. The static spin susceptibility components of armchair graphene nanoribbon have been calculated to find exchange interaction between arbitrary components of magnetic moments. We have exploited Green's function approach in order to calculate spin susceptibility components of electronic gas in nanoribbon structure in the context of tight binding model Hamiltonian. The effects of parameter and ribbon width on the dependence of exchange interaction on distance between moments are investigated. Our results show the spin polarization along perpendicular to the plane leads to anisotropic behavior for exchange interaction between the two magnetic moments. In other words the spatial behavior of RKKY interaction between longitudinal components of magnetic moments is different from that of transverse components. [ABSTRACT FROM AUTHOR]

We discuss the nonlinear Andreev current of an interacting quantum dot coupled to spin-polarized and superconducting reservoirs when voltage and temperature biases are applied across the nanostructure. Due to the particle-hole symmetry introduced by the superconducting (S) lead, the subgap spin current vanishes identically. Nevertheless, the Andreev charge current depends on the degree of polarization in the ferromagnetic (F) contact since the shift of electrostatic internal potential of the conductor depends on spin orientation of the charge carrier. This spin-dependent potential shift characterizes nonlinear responses in our device. We show how the subgap current versus the bias voltage or temperature difference depends on the lead polarization in two cases, namely (i) S-dominant case, when the dot-superconductor tunneling rate ( Γ ) is much higher than the ferromagnet-dot tunnel coupling ( Γ ), and (ii) F-dominant case, when Γ ≫ Γ . For the ferromagnetic dominant case the spin-dependent potential shows a nonmonotonic behavior as the dot level is detuned. Thus the subgap current can also exhibit interesting behaviors such as current rectification and the maximization of thermocurrents with smaller thermal biases when the lead polarization and the quantum dot level are adjusted. [ABSTRACT FROM AUTHOR]

The feasibility of generating polarized and unpolarized current in silicene by means of quantum pumping is discussed within the framework of Floquet scattering matrix. Charge pumping current is induced at zero magnetization splitting whereas spin and valley pumping current emerge when the symmetry between Dirac points K and K′ is broken. The intensity and direction of pumped current are shown to be dependent on pumping amplitude, phase between barriers, exchange energy and electric field. By careful control of external parameters, it is demonstrated that the ferromagnetic-silicene junction could be operated as a pump device that generates pure spin and valley pumping current. [ABSTRACT FROM AUTHOR]

We present a one-parameter family of mathematical models describing the dynamics of polarons in periodic structures, such as linear polypeptides, which, by tuning the model parameter, can be reduced to the Davydov or the Scott model. We describe the physical significance of this parameter and, in the continuum limit, we derive analytical solutions which represent stationary polarons. On a discrete lattice, we compute stationary polaron solutions numerically. We investigate polaron propagation induced by several external forcing mechanisms. We show that an electric field consisting of a constant and a periodic component can induce polaron motion with minimal energy loss. We also show that thermal fluctuations can facilitate the onset of polaron motion. Finally, we discuss the bio-physical implications of our results. [ABSTRACT FROM AUTHOR]

In Thouless pump, the charge transport in a one-dimensional insulator over an adiabatic cycle is topologically quantized. For nonequilibrium initial states, however, interband coherence will induce a previously unknown contribution to Thouless pumping. Though not geometric in nature, this contribution is independent of the time scale of the pumping protocol. In this work, we perform a detailed analysis of our previous finding [H.L. Wang et al., Phys. Rev. B 91, 085420 (2015)] in an already available cold-atom setup. We show that initial states with interband coherence can be obtained via a quench of the system's Hamiltonian. Adiabatic pumping in the post-quench system are then examined both theoretically and numerically, in which the interband coherence is shown to play an important role and can hence be observed experimentally. By choosing adiabatic protocols with different switching-on rates, we also show that the contribution of interband coherence to adiabatic pumping can be tuned. It is further proposed that the interband coherence induced correction to Thouless pumping may be useful in capturing a topological phase transition point. All our results have direct experimental interests. [ABSTRACT FROM AUTHOR]

By using first-principles calculations based on density-functional theory, the stability, magnetic and electronic properties of Fe and Co monoatomic chains encapsulated into copper nanotube are systematically investigated. The binding energies of the hybrid structures are remarkably higher than those of corresponding freestanding TM chains, indicating the TM chains are significantly stabilized after encapsulating into copper nanotube. The formed bonds between outer Cu and inner TM atoms show some degree of covalent bonding character. The magnetic ground states of Fe@CuNW and Co@CuNW hybrid structures are ferromagnetic, and both spin and orbital magnetic moments of inner TM atoms have been calculated. The magnetocrystalline anisotropy energies (MAE) of the hybrid structures are enhanced by nearly fourfold compared to those of corresponding freestanding TM chains, indicating that the hybrid structures can be used in ultrahigh density magnetic storage. Furthermore, the easy magnetization axis switches from that along the axis in freestanding Fe chain to that perpendicular to the axis in Fe@CuNT hybrid structure. The large spin polarization at the Fermi level also makes the hybrid systems interesting as good potential materials for spintronic devices. [ABSTRACT FROM AUTHOR]

We study perfect valley polarization in a molybdenum disulfide (MoS) nanoribbon monolayer using two bands Hamiltonian model and non-equilibrium Green's function method. The device consists of a one-dimensional quantum wire of MoS monolayer sandwiched between two zigzag MoS nanoribbons such that the sites A and B of the honeycomb lattice are constructed by the molecular orbital of Mo atoms, only. Spin-valley coupling is seen in energy dispersion curve due to the inversion asymmetry and time-reversal symmetry. Although, the time reversal symmetry is broken by applying an external magnetic field, the valley polarization is very small. A valley polarization equal to 46% can be achieved using an exchange field of 0.13 eV. It is shown that a particular spin-valley combination with perfect valley polarization can be selected based on a given set of exchange field and gate voltage as input parameters. Therefore, the valley polarization can be detected by detecting the spin degree of freedom. [ABSTRACT FROM AUTHOR]

Silver tungstate/iron phthalocyanine nanocomposite (AgWO/FePc) was prepared by simple solvent evaporation method. Thermodynamic stability of the synthesized nanocomposite was studied by thermogravimetric analysis. The nanocomposite was structurally characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. The results confirm the formation of AgWO/FePc nanocomposite. The size and morphology of the prepared nanocomposite were analyzed by scanning electron microscopy and high-resolution transmission electron microscopy. The optical properties were analyzed by ultraviolet-visible and photoluminescence spectroscopic techniques. UV-visible absorption studies indicate that AgWO/FePc nanocomposite has extended visible absorption in the wavelength range 662 to 782 nm. The nanocomposite shows high emission intensity and greenish-blue emission when excited with near-ultraviolet light. The resistivity of the sample was measured at different temperatures. The dielectric constant, dielectric loss and AC conductivity values were measured in the frequency range 100 Hz-20 MHz. The results obtained from thermal, structural, optical and electrical characterization suggests that the synthesized AgWO/FePc nanocomposite can be used as a potential material for varied optoelectronic and solid state applications. The present study constitutes the first report for the synthesis and characterization of AgWO/FePc nanocomposite. [ABSTRACT FROM AUTHOR]

A non-equilibrium Green's function formulation to study the spin transfer torque (STT) in non-collinear magnetic tunnel junctions (MTJs) exhibiting quasiparticle bands is developed. The formulation can be used to study the magnetoresistance and spin current too. The formulation is used to study the STT in model tunnel junctions exhibiting multiple layers and quasiparticle bands. The many body interaction that gives rise to quasiparticle bands is assumed to be a s − f exchange interaction at the electrode regions of the MTJ. The quasiparticle bands are obtained using a many body procedure and the single particle band structure is obtained using the tight binding model. The bias dependence of the STT as well as the influence of band occupancy and s − f exchange coupling strength on the STT are studied. We find from our studies that the band occupancy plays a significant role in deciding the STT and the s − f interaction strength too influences the STT significantly. Anomalous behavior in both the parallel and perpendicular components of the STT is obtained from our studies. Our results obtained for certain values of the band occupation are found to show the trend observed from the experimental measurements of STT. [ABSTRACT FROM AUTHOR]

We calculate the dispersion laws of plasma oscillations for the quasi-one-dimensional multisubband non-degenerate charge system realized in a conducting electron channel over the surface of liquid helium. The influence on plasma dispersion from an external magnetic field is considered. A novel two-subband approach within the random-phase approximation is employed for both intra- and intersubband plasmons. Our results are compared with those obtained previously in quasi-crystalline approach; despite being qualitatively similar, there are quantitative differences, especially at high wave numbers. [ABSTRACT FROM AUTHOR]

The electronic properties and optical characteristics - absorption coefficient, refractive index and group index - in an impurity doped pseudo-harmonic quantum disc subjected to an applied magnetic field are investigated. Numerical calculations are performed using the exact diagonalization technique and the compact density-matrix formalism. It is found that the chosen structure could be switched between a lambda-type and a ladder-type configuration by a proper tailoring of the magnetic field strength. Furthermore, the absorption profile and the associated slow light frequency range can be controlled not only by varying the control field amplitude and its detuning but also by changing the impurity position and the magnetic field strength. [ABSTRACT FROM AUTHOR]

Prussian blue analogues (PBA) ferromagnetic nanoparticles Cs Ni[Cr(CN) ]·3(HO) embedded in CTA (cetyltrimethylammonium) matrix have been investigated by magnetometry and magnetic small-angle neutron scattering (SANS). Choosing particle sizes (diameter D = 4.8 and 8.6 nm) well below the single-domain radius and comparable volume fraction of particle, we show that the expected superparamagnetic regime for weakly anisotropic isolated magnetic particles is drastically affected due to the interplay of surface/volume anisotropies and dipolar interactions. For the smallest particles ( D = 4.8 nm), magnetocrystalline anisotropy is enhanced by surface spins and drives the system into a regime of ferromagnetically correlated clusters characterized by a temperature-dependent magnetic correlation length L which is experimentally accessible using magnetic SANS. For D = 8.6 nm particles, a superparamagnetic regime is recovered in a wide temperature range. We propose a model of interacting single-domain particles with axial anisotropy that accounts quantitatively for the observed behaviors in both magnetic regimes. [ABSTRACT FROM AUTHOR]

Here, we employ a numerical approach to investigate the transport and conductance characteristics of a quantum point contact. A quantum point contact is a narrow constriction of a width comparable to the electron wavelength defined in a two-dimensional electron gas (2DEG) by means of split-gate or etching technique. Their properties have been widely investigated in the experiments. In our study, we define a quantum Hall based split-gate quantum point contact with standard gate geometry. Firstly, we obtain the spatial distribution of incompressible strips (current channels) by applying a self consistent Thomas-Fermi method to a realistic heterostructure under quantized Hall conditions. Later, time-dependent Schrödinger equation is solved for electrons injected in the current channels. The transport characteristics and time-evolutions are analyzed in the integer filling factor regime ( ν = 1) with the single electron density. The results confirm that the current direction in a realistic quantum point contact can be controllable with the external interventions. [ABSTRACT FROM AUTHOR]

We investigate the effect of spatial disorder on the edge states localized at the interface between two topologically different regions. Rotation disorder can localize the quantum walk if it is strong enough to change the topology, otherwise the edge state is protected. Nonlinear spatial disorder, dependent on the walker's state, attracts the walk to the interface even for very large coupling, preserving the ballistic transport characteristic of the clean regime. [ABSTRACT FROM AUTHOR]

The quantum spin Hall (QSH) effect and the quantum anomalous Hall (QAH) effect in Lieb lattice are investigated in the presence of both Rashba spin-orbit coupling (SOC) and uniform exchange field. The Lieb lattice has a simple cubic symmetry, which is characterized by the single Dirac-cone per Brillouin zone and the middle flat band in the band structure. The intrinsic SOC is essentially needed to open the full energy gap in the bulk. The QSH effect could survive even in the presence of the exchange field. In terms of the first Chern number and the spin Chern number, we study the topological nature and the topological phase transition from the time-reversal symmetry broken QSH effect to the QAH effect. For Lieb lattice ribbons, the energy spectrum and the wave-function distributions are obtained numerically, where the helical edge states and the chiral edge states reveal the non-trivial topological QSH and QAH properties, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we carried out first-principles calculations based on density functional theory and non-equilibrium Green's function to investigate the electronic transport properties of a quinone-based molecule sandwiched between two Au electrodes. The molecular switch can be reversibly switched between the reduced hydroquinone (HQ) and oxidized quinone (Q) states via redox reactions. The switching behavior of two forms is analyzed through their I- V curves, transmission spectra and molecular projected self-consistent Hamiltonian at zero bias. Then we discuss the transmission spectra of the HQ and Q forms at different bias, and explain the oscillation of current according to the transmission eigenstates of LUMO energy level for Q form. The results suggest that this kind of a quinone-based molecule is usable as one of the good candidates for redox-controlled molecular switches. [ABSTRACT FROM AUTHOR]

Fisher-Lee relation \hbox{$\bm{t}= {i}\bm{\Gamma}_L^{1/2}\bm{G}\bm{\Gamma}^{1/2}_R$} t = i Γ L 1 / 2 G Γ R 1 / 2 is a well-established tool to decode the mode information from Green's function and coupling parameters. Using the Bloch eigen-modes of the leads, we show that the \hbox{$\bm{\Gamma}^{1/2}_{L/R}$} Γ L / R 1 / 2 term can be expressed by the Bloch eigen-mode vectors and the wave velocities which give unambiguous algorithm of \hbox{$\bm{\Gamma}^{1/2}_{L/R}$} Γ L / R 1 / 2 in the Fish-Lee relation. Using this approach, we present an accurate and convenient technique to analyze all transport modes and also the dominant channels of an electronic transport system in tight-binding model. We study graphene nanoribbon structures to demonstrate the typical application of our technique. [ABSTRACT FROM AUTHOR]

Using the Green's function technique, we respectively investigate the electron transport properties of two spin components through the system of a T-shaped double quantum dot structure coupled to a Majorana bound state, in which only one quantum dot is connected with two metallic leads. We explore the interplay between the Fano effect and the MBSs for different dot-MBS coupling strength λ, dot-dot coupling strength t, and MBS-MBS coupling strength ε in the noninteracting case. Then the Coulomb interaction and magnetic field effect on the conductance spectra are investigated. Our results indicate that G( ω) is not affected by the Majorana bound states, but a '0.5' conductance signature occurs in the vicinities of Fermi level of G( ω). This robust property persists for a wide range of dot-dot coupling strength and dot-MBS coupling strength, but it can be destroyed by Coulomb interaction in quantum dots. By adjusting the size and direction of magnetic field around the quantum dots, the '0.5' conductance signature damaged by U can be restored. At last, the spin magnetic moments of two dots by applying external magnetic field are also predicted. [ABSTRACT FROM AUTHOR]

We investigated the combined effects of a non-resonant intense laser field and a static electric field on the electronic structure and the nonlinear optical properties (absorption, optical rectification) of a GaAs asymmetric double quantum dot under a strong probe field excitation. The calculations were performed within the compact density-matrix formalism under steady state conditions using the effective mass approximation. Our results show that: (i) the electronic structure and optical properties are sensitive to the dressed potential; (ii) under applied electric fields, an increase of the laser intensity induces a redshift of the optical absorption and rectification spectra; (iii) the augment of the electric field strength leads to a blueshift of the spectra; (iv) for high electric fields the optical spectra show a shoulder-like feature, related with the occurrence of an anti-crossing between the two first excited levels. [ABSTRACT FROM AUTHOR]

We investigate the properties of persistent charge current driven by magnetic flux in a quasi-periodic mesoscopic Fibonacci ring with Rashba and Dresselhaus spin-orbit interactions. Within a tight-binding framework we work out individual state currents together with net current based on second-quantized approach. A significant enhancement of current is observed in presence of spin-orbit coupling and sometimes it becomes orders of magnitude higher compared to the spin-orbit interaction free Fibonacci ring. We also establish a scaling relation of persistent current with ring size, associated with the Fibonacci generation, from which one can directly estimate current for any arbitrary flux, even in presence of spin-orbit interaction, without doing numerical simulation. The present analysis indeed gives a unique opportunity of determining persistent current and has not been discussed so far. [ABSTRACT FROM AUTHOR]

We present analytical expressions for the eigenstates and eigenvalues of electrons confined in a graphene monolayer in which the crystal symmetry is locally modified by replacing a hexagon by a pentagon, square or heptagon. The calculations are performed in the continuum limit approximation in the vicinity of the Dirac points, solving Dirac equation by freezing out the carrier radial motion. We include the effect of an external magnetic field and show the appearance of Aharonov-Bohm oscillations and find out the conditions of gapped and gapless states in the spectrum. We show that the gauge field due to a disclination lifts the orbital degeneracy originating from the existence of two valleys. The broken valley degeneracy has a clear signature on quantum oscillations and wave packet dynamics. [ABSTRACT FROM AUTHOR]

We explore the stability of a Wigner molecule (WM) formed in confinements with different geometries emulating the role of disorder and analyze the melting (or crossover) of such a system. Building on a recent calculation [D. Bhattacharya, A. Ghosal, Eur. Phys. J. B 86, 499 (2013)] that discussed the effects of irregularities on the thermal crossover in classical systems, we expand our studies in the untested territory by including both the effects of quantum fluctuations and of disorder. Our results, using classical and quantum (path integral) Monte Carlo techniques, unfold complementary mechanisms that drive the quantum and thermal crossovers in a WM and show that the symmetry of the confinement plays no significant role in determining the quantum crossover scale n. This is because the zero-point motion screens the boundary effects within short distances. The phase diagram as a function of thermal and quantum fluctuations determined from independent criteria is unique, and shows 'melting' from the WM to both the classical and quantum 'liquids'. An intriguing signature of weakening liquidity with increasing temperature, T, is found in the extreme quantum regime. The crossover is associated with production of defects. However, these defects appear to play distinct roles in driving the quantum and thermal 'melting'. Our analyses carry serious implications for a variety of experiments on many-particle systems − semiconductor heterostructure quantum dots, trapped ions, nanoclusters, colloids and complex plasma. [ABSTRACT FROM AUTHOR]

In this work, we investigated the nonadiabatic transport properties of the one-dimensional time-dependent superconductor-normal metal-superconductor (SNS) Josephson junction biased by a current source and driven by a high-frequency-ac-gate-potential applied to the normal-metal layer. BCS superconductors are considered and treated with the time-dependent Bogoliubov-de Gennes equation. Using Floquet theory, we compute the transmission coefficients and the Wigner-Smith delay times as a function of the incident energy and find that they display resonances when one of the electron or hole Floquet wavevectors coincides with the bound quasiparticle state within the superconducting energy gap. The resonance varies with the phase difference between the two superconductors as a result of the bound quasiparticle level displacement. The supercurrent flowing through the SNS junction is dramatically enhanced by the resonances. [ABSTRACT FROM AUTHOR]