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The electron effective mass in GaAs quantum wires has been estimated by using a full dynamical random-phase approximation to examine its properties versus spin polarization, temperature, and carrier density. A decrease of mass with spin polarization is seen. The minority mass increases with the polarization while the majority mass decreases and this behaviour is seen for all densities. A maximal enhancement of mass at moderate temperature around 25 K is also presented. These calculations show a qualitative consistence with results in two-dimensional systems and help to control the electronic transport in quantum wires.

We investigate the transfer of genuine multipartite entanglement across a spin-1/2 chain with nearest-neighbor XX-type interaction. We focus on the perturbative regime, where a block of spins is weakly coupled at each edge of a quantum wire, embodying the role of a multiqubit sender and receiver, respectively. We find that high-quality multipartite entanglement transfer is achieved at the same time that three excitations are transferred to the opposite edge of the chain. Moreover, we find that both a finite concurrence and tripartite negativity is attained at much shorter time, making GHZ-distillation protocols feasible. Finally, we investigate the robustness of our protocol with respect to non-perturbative couplings and increasing lengths of the quantum wire., Comment: Comments welcome

Spin transport properties in a non-uniform quantum wire (QW) in the presence of both the Rashba and Dresselhaus spin–orbit couplings (SOCs) is investigated by using the non-equilibrium Green's function (NEGF) method combined with the Landauer Buttiker formalism. It is found that such a non-uniform quantum wire exhibits considerable spin polarization in its conductance in the influence of both the Rashba and Dresselhaus SOCs, and that the two SOCs' strengths strongly affect both the magnitude and sign of the electron spin polarization. Interestingly, the Rashba and Dresselhaus SOCs play the same modulating role in the electron spin polarization. The proposed nanostructure can potentially be utilized to devise an all-electrical spintronic device.

In this work, we investigate GaSb / InAs 1 − x N x T-shaped quantum wire active region in mid-infrared laser. Multi-band k.p model and variational formalism are applied to find the confinement energies, the band structures, and optical gain. We then present a method of numerical calculation that is suited to any T-shaped quantum wire. By tuning the quantum wire thickness, the TE- and TM-polarized optical gain up to 21 × 10 3 cm − 1 can be obtained for λ = 3.11 μm at room temperature (RT), which is very promising to serve as an alternative active region for high-efficiency mid-infrared laser applications.

We investigate ballistic transport phenomena through a region containing a cavity in a quasi-one-dimensional quantum wire. Conductance curve calculated as a function of a structure parameter shows very narrow periodic dips, which are due to anti-resonances. The nature of the virtual bound state appearing around the cavity is studied in detail. Transport phenomena through a small dilute magnetic semiconductor are also investigated.

The propagation of bulk and surface plasma waves in a thin quantum plasma film is investigated, taking into account the quantum effects. The generalized bulk and surface plasma dispersion relation due to quantum effects is derived, using the quantum hydrodynamic dielectric function and applying appropriate additional boundary conditions. The quantum mechanical and film geometric effects on the bulk and surface modes are discussed. It is found that quantum effects become important for a thin film of small thickness.

We study theoretically the effect of a pure spin current in a quantum wire on magnetic domain walls (DWs). We find that a pure spin current acts on DWs with an effective spin-transfer torque that depends on the mutual DWs separation which results in picosecond magnetization dynamics. Spin-dependent interferences due to spin-current scattering from DWs result in a spin-orbital interaction of the carriers whose strength is determined by the orientations and the spatial separation of DWs. This amounts to an effective dynamical magnetoelectric coupling.

By the use of the scattering matrix method, we investigate the effect of evanescent modes on acoustic phonon transport and thermal conductance in both convex and concave type three-dimensional quantum wire. Our results show that the evanescent modes can enhance the transmission coefficient and the thermal conductance in the concave type three-dimensional quantum wire. However, for the convex type three-dimensional quantum wire, the evanescent modes can play adverse effect on the phonon transport. When the length of scattering region is large enough, for all types of three-dimensional quantum wire, the influence of evanescent modes on phonon transport becomes very weak.

We study the ballistic phonon transport and thermal conductance of six low-lying vibration modes in quantum wire modulated with quantum dot at low temperatures. A comparative analysis is made among the six vibrational modes. The results show that the transmission rates of the six vibrational modes relative to reduced frequency display periodic or quasi-periodic oscillatory behavior. Among the four acoustic modes, the thermal conductance contributed by the torsional mode is the smallest, and the thermal conductances of other acoustic modes have adjacent values. It is also found that the thermal conductance of the optical mode increases from zero monotonously. Moreover, the total thermal conductance in concavity-shaped quantum structure is lower than that in convexity-shaped quantum structure. These thermal conductance values can be adjusted by changing the structural parameters of the quantum dot.

In this paper, we derive an analytical expression for the screened Coulomb potential between charge carriers in quasi-one-dimensional (Q1D) semiconductor structures. As an application, this potential has been used to investigate the screening effect on the binding energy of a neutral donor ( D 0 ) in quantum wires (QWRs). It is found that the screening effect decreases the neutral donor binding energy, and the screening effects are more obvious in wide QWRs than that in narrow ones. Dependence of screening length on temperature and carrier concentration has also been discussed.

It was recently reported that a kind of graphene line defect can be fabricated in a controllable experimental way. In the present work we theoretically investigate the band structure and the electronic transport properties of a graphene superlattice formed by embedding periodically line defects in the graphene lattice. Based on the calculated results, we suggest that such a superlattice can be used as a quantum wire array which can carry much larger current than a single graphene nanoribbon. A remarkable advantage of this superlattice over other quantum wires is that the electronic transport in it is insensitive to scattering effects except that the scattering potential range is smaller than the graphene lattice constant. Moreover, we find that the anisotropy of the Dirac cone presented in this superlattice has a nontrivial influence on the universal minimal conductivity and the sub-Poissonian shot noise of graphene.

The properties of scattering phases and density of states in a quantum wire with an attractive scatterer are analyzed. We consider two bound states which couple to a scattering channel and give rise to two Fano resonances. It is shown that varying the parameters of the scatterer (such as its strength and position) produces significantly different effects on the phase behavior and density of states, depending on the subband they occur. These effects stem mainly from the difference between the coupling matrix elements of the two resonant levels with the propagating channel mode.

We present a finite difference calculation of the binding energies of localized trions in quasi-one-dimensional quantum wires (QWRs). It is found that both the lateral confinement and the localization potential have a strong effect on the relative stability of the trions. It is confirmed that a weak localization potential not only enhances the binding energy but also changes the relative stability of the positive and negative trions. Our theoretical model is in good accord with a recent experiment regarding photoluminescence in disordered QWRs.

Under the dielectric continuum model and separation of variables, the interface optical (IO) phonon modes and electron–optical-phonon interaction in rectangular quantum wire and quantum dot embedded in a nonpolar matrix are studied. We found that there exist various types of IO phonon modes in rectangular nanostructures. The IO phonon modes in rectangular quantum wire include IO–propagating (IO–PR) and IO–IO hybrid phonon modes, while the IO phonon modes in rectangular quantum dot contain IO–IO–PR and IO–PR–PR hybrid phonon modes. The results of numerical calculation show that these hybrid phonon modes contain corner optical (CO) phonon modes and edge optical (EO) phonon modes. The potential applications of these results are also discussed.

Transport property of superconductive armchair graphene ribbon (AGR) connected to quantum-wire (QW) contacts is investigated via Landauer formalism combined with transfer matrix method. The scattering at the AGR/QW interface induces an obvious asymmetry in conductance as gate voltage varies. The transmission peak is located at momentum k y = 2 π 3 3 a with a = 0.142 nm . Andreev reflection (AR) enhances electronic transmission in the presence of hole reflection process. At lowest carrier density, the conductance of AGR in superconductive state becomes constant while the counterpart of semiconductive AGR in normal state decays exponentially with the length. The conductance increases with pair potential at low carrier density. The interplay between superconductivity and the scattering at the AGR/QW interface guides future application of superconductive graphene ribbon.

We investigate theoretically the spin-polarized electron transport for a wide-narrow-wide (WNW) quantum wire under the modulation of Rashba spin-orbit interaction (SOI). The influence of both the structure of the quantum wire and the interference between different pairs of subbands on the spin-polarized electron transport is taken into account simultaneously via the spin-resolved lattice Green function method. It is found that a very large vertical spin-polarized current can be generated by the SOI-induced effective magnetic field at the structure-induced Fano resonance even in the presence of strong disorder. Furthermore, the magnitude of the spin polarization can be tuned by both the Rashba SOI strength and structural parameters. Our results may provide an effective way to design a spin filter device without containing any magnetic materials or applying a magnetic field., Comment: 7 pagesm, 6 figures

We study nonlocality effects of a bulk plasmalike dielectric medium on the plasmon spectrum of a one-dimensional (1D) quantum wire superlattice in interaction with the 3D nonlocal host bulk plasma, by carrying out a closed-form analytic determination of the inverse dielectric function ? for the joint nanostructure system within the random phase approximation (RPA), in which we treat nonlocality of the 1D superlattice in the RPA and that of the bulk medium in the hydrodynamic model. By examining the frequency poles of ? (i.e., the dispersions relations), we show analytically that coupled plasmon modes of the interacting 1D superlattice-3D nonlocal host are damped in high frequencies (damping is pronounced near resonance region) and that nonlocality of the host medium introduces nonlocal low frequency (real) modes into the spectrum, which have cutoff frequencies for finite wave vector values. In order to describe the impact of nonlocality effects more clearly, we also examine the spectrum numerically. © 2009 Elsevier B.V. All rights reserved.

The confined longitudinal-optical (LO) phonon and surface-optical (SO) phonon modes of a free-standing quantum wire with ring geometry are discussed within the dielectric continuum (DC) approximation. Two branches of SO phonon modes have been investigated. The frequencies of the SO phonons are found to be dispersed and radius dependent for small size systems. When the wave vector q z → ∞ , the frequencies of each SO modes converge to the frequency values of the single planar heterostructure.

The intent of this work is to develop a more generalized approach towards strain field calculations in embedded quantum wires (QWRs). Higher degree polynomials are used to achieve better discretization of QWR in arbitrary shapes and to avoid some of the singular points in the strain field calculations. Calculations are performed for simpler geometries such as triangular and square shaped QWRs to verify the validity of the approach. The same approach is tested for more complicated shapes such as crescent shaped QWRs with and without lateral quantum wells. The strain field distributions, are observed to be similar to those obtained from the analytical expressions. However, in the case of crescent shaped QWRs, the strain distribution is different in the region above the QWR. The difference is the result of the better discretization and of the removed singular points. The use of higher degree polynomials provides better discretization for shapes of interest.

We study theoretically the dwell time for electrons travelling through a quantum wire irradiated under a transversely-polarized external electromagnetic field. Using the semiclassical method of an atom interaction with single-mode field originally proposed in quantum optics, we obtain a two-level electron-field interaction wavefunction in the framework of free-electron approximation. Consequently, using this wavefunction the electron dwell time through the quantum wire is calculated in accord with transport property.

Using the scattering-matrix method, we investigate the acoustic phonon transmission and thermal conductance in a multiple channels nanostructure at low temperature. Our results show that phonon transport is strongly influenced by mode coupling effect between channels, and the effect is different for different types of boundary conditions between channels.

The scattering intensity (SI) of a free-standing cylindrical semiconductor quantum wire for an electron resonant Raman scattering (ERRS) process associated with bulk longitudinal optical (LO) phonon modes and surface optical (SO) phonon modes is calculated separately for T = 0 K . The Frohlich interaction is considered to illustrate the theory for GaAs and CdS systems. Electron states are confined within a free-standing quantum wire (FSW). Single parabolic conduction and valence bands are assumed. The selection rules are studied. Numerical results and a discussion are also presented for various radii of the cylindrical.

Transport through a quantum wire sandwiched between two metallic electrodes and coupled to a quantum ring, threaded by a magnetic flux ϕ , is studied. An analytic approach for the electron transport through the bridge system is presented based on the tight-binding model. The electronic transport properties are discussed in three aspects: (a) the presence of external magnetic filed, (b) the strength of the wire to electrodes coupling and (c) the presence of in-plane electric field.

Using the scattering-matrix method, we investigate the influences of boundary conditions on thermal conductance in quantum wire with structural defect. A comparison between the thermal conductances is made when stress-free, hard-wall, and mixed boundary conditions are applied for acoustic transport leads. The results show that the quantized thermal conductance plateau at very low temperature can be observed only in transport lead with stress-free boundary condition. For hard-wall or mixed boundary conditions, qualitatively different thermal conductance characteristics are found. Moreover, we find that the behavior of the thermal conductance sensitively depend on the geometric parameters and the position of the defect in quantum wire.

We investigate quantum motions of an electron driven by a strong time-dependent linear potential in a one-dimensional (1D) quantum wire. An exact n wave-packet-train solution of Gaussian-type is constructed, whose center moves acceleratively along the corresponding classical trajectory. It is shown that the single Gaussian wave-packet solution recently reported by Luan and Tang [P.-G. Luan, C.-S. Tang, Phys. Rev. A 71 (2005) 014101] is the special case n = 0 of our result. The interesting physical properties described by the n wave-packet-train solution are studied, which concern the nearly squeezing coherence property of the wave-function, the band structure of average energy composed of quantum levels and classical oscillations, and the probability densities spreading and collapsing like that of a free particle.

We study the effect of generation and amplification of confined acoustic phonons by drifting electrons in an embedded quantum wire. A general formula for the phonon amplification coefficient α has been derived. Our calculations show that the quantum wire structure can be used for electrical generation of an intense high-frequency coherent phonon flux. The amplification coefficients of the order of cm−1 can be achieved in the sub-THz range for the example of Si0.5Ge0.5 quantum wires embeded in Si.

Electron transport in a crossed nano-wire junction is studied using a tight-binding model. Increase in the inter-wire tunneling coupling strength suppresses the transmissions through the junction around the first subband edge. The junction's transport characteristics can be explained by the formation of bound or quasi-bound states at the junction.

Using an efficient expanded basis method, we have studied the effects of Rashba spin–orbit interaction (SOI) and a laterally inhomogeneous magnetic field on the eigenstates of spin-polarized electrons in a quantum wire. Our numerical results show that inhomogeneous magnetic field can significantly modify the energy spectrum as compared with uniform magnetic field. The spatial distributions of probability and spin densities across the wire have also been investigated. We find that in the presence of only Rashba SOI, i.e., without magnetic field, the component of spin density parallel to the propagating direction vanishes for all the states and the other two spin components exhibit even (or odd) symmetry and oscillating behaviors across the wire. Under the interplay of Rashba SOI and nonuniform magnetic field, the distributions of both the probability and spin densities show a variety of localized behavior. The spin polarizations of electrons strongly depends on the wave number of the propagating state.

The charge pumping is investigated in a quasi-one-dimensional quantum wire within an external perpendicular magnetic field. A formula of the pumped current at finite frequency is derived by using scattering matrix method. It is found that the pumped current oscillates with the magnetic field due to Aharonov–Bohm effect and the oscillating period is only dependent on the effective area enclosed by two pumping potentials. At a weak magnetic field, the pumped current also exhibits an approximate magnetic field inversion symmetry.

The approach to take into account the influence of the energy levels broadening on the intersubband acoustic phonon scattering rates is developed. The roughness of the quantum wire boundaries and the oscillations of crystal lattice atoms are treated as the mechanisms causing the energy levels broadening. It is shown that the function of intersubband acoustic phonon scattering rate versus electron kinetic energy has no singularity points.

We study the transport properties of independent carriers through a quantum wire coupled to a quantum-dot array. The electrical conductance at zero temperature can be expressed through a non-linear discrete dynamical system as the number of quantum dots varies. The dynamical system shows a rich behavior, determining a non-trivial conductance dependence on the Fermi energy. The conductance depends smoothly on the Fermi energy far from the site-energy of the quantum dots. At the center of the band the conductance develops a complex pattern due to constructive and destructive interference in the ballistic channel.

A complete band structure is shown to exist for one-dimensional periodic non-Hermitian potentials exhibiting PT-symmetry. The full band spectrum is exactly given and some of its properties discussed, specially those concerning the role of the imaginary parameters of the couplings. Infinite periodic arrays constructed with finite chains each one made of N different ultralocal couplings are used as models of this one-dimensional complex quantum wire.

Using the tight-binding calculations, we have studied electronic and transport properties of the semiconducting single-walled carbon nanotubes (SSWNTs) doped by a chain of carbon-atoms, which can be well controlled by density of the encapsulated carbon atoms. When it is lower, weak coupling between the chain atoms and the tube produces flat bands near the Fermi level, which means a great possibility of superconductivity and ferromagnetism for the combined system. The weak coupling also leads to a significant conductance at the Fermi level, which is contributed by both of the tube and the encapsulated carbon-atom chain. Increasing density of the chain carbon atoms, the flat bands near the Fermi level disappear, and the current may be carried only by the carbon-atom chain, thus making the system become an ideal one-dimensional quantum wire with its conducting chain enclosed by a SWNT insulator.

We present a theoretical investigation of a phase transition between ferromagnetic and paramagnetic phases of III-Mn-V diluted magnetic semiconductor quantum wires. The critical temperature T c of the ferromagnetic phase in a diluted magnetic semiconductor quantum wire is inversely proportional to the one-dimensional carrier density and is enhanced by the hole–hole exchange energy F xc .

Many electrons tunneling through strong Hubbard interacting quantum dots in applied magnetic field is studied numerically. It is found that the oscillations in conductance and magnetization exhibit a class of new universal quantum oscillations. In particular, the periodic conductance oscillations as a function of magnetic field are predicted and agree qualitatively with experimental measurements.

We report the temperature dependence of the photoluminescence from our V-grooved GaAs/AlGaAs quantum wires. Based on the specially resolved luminescence results, our results show that in the processes of real space carrier transfer from the vertical quantum well region to quantum wire region. a 3.5 meV thermal activation energy has been experimentally observed in our sample. The thermal activation is attributed as the scattering process of carriers from two-dimensional states in the vertical quantum well to the one-dimensional quantum wire states. Based on numerical energy band structure analysis, a thermal activation energy of 2-9 meV is obtained theoretically, in good agreement with the experimental data. (C) 2001 Elsevier Science B.V. All rights reserved.