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In this work, we study the effects of the Rashba spin-orbit interaction (SOI) and applied magnetic field on thermodynamic properties of a quasi-one-dimensional quantum wire at low temperatures. To this end, we first present an explicit relation for partition function. Then, we give analytical expressions for the mean energy, specific heat, free energy, and entropy of the system. It is found that the specific heat shows a peak structure in the presence of SOI and then reduces to zero. The peak width of the specific heat depends on the strength of SOI. At low temperatures, the entropy reduces with increasing magnetic field in the presence of SOI, but at higher temperatures, it remains almost independent of the magnetic field. The peak of specific heat occurs at a certain value of the magnetic field which depends on the temperature.

We report experiments on the two-terminal conductance of a long disordered quantum wire in a perpendicular magnetic field. Pronouncedly enhanced magnetoconductance in magnetic fields of intermediate strength is observed in the Coulomb blockade regime, which is well explained using the boundary roughness scattering and the subband quantization of the quantum wire, by modeling the disordered quantum wire as that of a quantum dot defined in a quantum wire. Assuming a parabolic constriction in the disordered quantum wire, we further obtained the magnetic field dependence of high energy levels in the quantum dot and the gate voltage dependence of the effective width of the quantum wire. Our results may provide useful information for further studies on integrated structures in on-chip laboratories.

In this paper, the influence of impurity parameters on the energy-dispersion spectrum of electrons and holes in a doped quantum wire with Gaussian impurity is studied. The numerical calculations have shown that the energy eigenvalues enhance, if the confinement of carriers increases. Then, the energy eigenvalues rise when the magnetic field, decay length and strength of impurity increase. Also, the type of impurity affects the energy subband structures. So that, the presence of attractive impurity reduces the energy eigenvalues, as compared to repulsive impurity. Moreover, the role of impurity parameters and the external magnetic field as a control parameter on the thermal quantities has been demonstrated in details. The results show that enhancement of magnetic field, decay length and strength of repulsive impurity decreases (increases) the entropy (internal energy) of quantum wire.

We study a thin-film quantum wire/unconventional superconductor junction in the presence of an intrinsic exchange field for a d-wave symmetry of the superconducting order parameter. A strongly spin-polarized current is generated due to an interplay between Zeeman splitting of bands and the nodal structure of the superconducting order parameter. We show that strongly spin-polarized current is achievable for both metallic and tunnel junctions. This is because of the presence of a quantum wire (one-dimensional metal) in our junction. While in two-dimensional junctions with both conventional [F. Giazotto, F. Taddei, Phys. Rev. B 77 (2008) 132501] and unconventional [J. Linder, T. Yokoyama, Y. Tanaka, A. Sudbo, Phys. Rev. B 78 (2008) 014516] pairing states, highly spin polarized current takes place just for a tunnel junction. Also, the obtained spin-polarized current is tunable in sign and magnitude in terms of exchange field and applied bias voltage.

We present a detail analysis of the elastic energy, derive analytical expressions of the elastic self-relaxation energy and interaction energy, for coherently strained quantum wires of a triangular section grown on a substrate, and use these results to calculate the chemical potential of the wire, which serves as the base of the thermodynamic stability and dynamical evolution analysis of elastically interacting quantum wire arrays.

We have provided a complete description of the electron localization length (LL) in quasi-one dimensional (Q1D) disordered quantum wire with hard wall and periodic boundary conditions. Presented analytical expressions for LL are in excellent agreement with numerical calculations, exact up to order W2 (W being the disorder strength), and valid for an arbitrary number of propagating and evanescent channels. We have calculated the average conductance in Q1D systems, establish relationship between various lengths and show that it basically differs from 1D case.

We calculate hole energies of the bonding and antibonding states in coupled quantum wires using 6-band kp model. It is shown that hole ground state changes character from a bonding to an antibonding orbital with increasing inter-wire distances. This effect is a consequence of the enhancement of light hole contribution to the ground state. The variations of g factors under external electric and magnetic fields demonstrate the antibonding character of hole ground states.

We study theoretically the alternating current (ac) transport property through a two-channel clean quantum wire of finite length in the presence of both inter-channel and intra-channel electron–electron (e–e) interactions. Using the bosonization technique and linear response theory, we have obtained analytical expressions of the ac conductance. Interestingly, the ac conductance oscillations, with two different frequencies, form a beat which governs the behavior of the transport property in the presence of inter-channel e–e interaction. This result provides us with a new way to control the transport property of narrow quantum wires by engineering the Fermi velocities in the two different channels, i.e., the electron density.

We investigate the theoretically combined effect of spin–orbit interactions and Coulomb interaction on the ground state and transport property of a quantum wire oriented along different crystallographic directions in the (110) plane. We find that the electron’s ground state exhibits phase transition among spin density wave, charge density wave, singlet superconductivity and metamagnetism, which can be controlled by changing the crystallographic orientation, the strengths of the spin–orbit interactions and the Coulomb interaction. The ac conductance exhibits a significant anisotropic behavior and a out-of-plane spin polarization which can be tuned by an in-plane electric field.

In this study, we extend a fully exact Green’s function formalism to calculate the phonon transmission coefficient in a short simulated chain. We obtain new analytical formulas for a uniform-mass and periodic-mass chain. The results for a simple chain show that the resonance peak will be appeared without gap but for the periodic chain the transmission coefficient contains a gap in the acoustic band of leads.

The tunneling conductance in a normal metal/insulator/metal/ d x 2 − y 2 + i d x y mixed wave superconductor (N/I/N/ d x 2 − y 2 + i d x y ) junction is calculated, where the N/I/N region is a quantum wire. It is found in the single-mode case that the magnitude of the tunneling conductance near zero voltage is enhanced due to the Andreev bound state by quasiparticles with perpendicular and horizontal injection, and the zero-bias conductance varies with L ( L is the distance from insulating layer to the interface of N/ d x 2 − y 2 + i d x y mixed wave superconductor). Splitting of the zero-bias conductance peak appears in the quantum point contact tunneling spectra for an N/I/N/ d x 2 − y 2 + i d x y junction, and several subgap peaks can split at the same time. On increasing both L and the magnitude ratio of the two components for the d x 2 − y 2 + i d x y mixed wave, the subgap resonances exhibit an alternately high and low behavior inside the energy gap. These results are different from those in d-wave and p-wave superconductor junctions.

The effects of a linearly polarized, terahertz laser field on the density of states (DOS) for carriers confined in a cylindrical semiconductor quantum wire are investigated here within a nonperturbative scheme, based upon a Green’s function approach. In our model, the functional dependence of the DOS on energy is significantly modified in two ways: (i) an uniform blueshift with respect to the laser-free DOS; and (ii) a strong suppression, with the appearance of Franz–Keldysh-like oscillations. Interestingly, with the increase (decrease) of the laser intensity (frequency) the DOS profile evolves from the usual shape for one-dimensional (1D) systems to a discrete set of sharp peaks that resembles the DOS for quasi-zero-dimensional (quasi-0D) electrons confined in quantum dots.

In the framework of the Blonder–Tinkham–Klapwijk model we have studied the quasiparticle transport in normal-metal/insulator/metal/p wave superconductor Junction (N/I/N/p), where the N/I/N region is a quantum wire. We calculate the quantum point contact conductance in N/I/N/p as a function of the bias voltage at zero temperature based on the Bogoliubov–de Gennes equations. Unlike the case in N/I/N/d superconductor junctions, the zero-bias conductance peaks appear in the single-mode case. The number of resonances for the quantum point contact differential conductance for the px wave superconductor is different from that for the py wave superconductor.

Soft ZnSe nanobelts were synthesized by taking Triton X-100 as the template surfactant in a microemulsion. Orderly alternating grooves and bulges on the surface of the nanobelts were first observed via TEM images, and potentially divide a nanobelt into quantum wire bundles. We found that the as-prepared nanobelts show remarkable varied photon scattering and optical properties. A tubular ZnSe structure was successfully obtained with extra treatment. This is an important phenomenon because that the regular folded nanobelts should help us to understand the plastic mechanical properties in a nanoscale assembled tubular structure of nanomaterials and modulate the optical properties of semiconductors.

An all-coupling variational calculation based on Lee-Low-Pines-Huybrechts (LLPH) theory is performed to study the ground state and the first excited state in an asymmetric polar semiconductor quantum wire that is valid for the entire range of the electron-phonon coupling constant and arbitrary confinement length. It is shown that the polaronic effects are very important and size dependent, if the effective width of the wire is reduced below a certain length scale. It is also shown that asymmetry in a quantum wire can be used as an extra parameter to increase the stability of the polaron. Finally the theory is applied to a realistic CdS quantum wire.

We investigate the spin-flip effect on electronic transport in a nanostructure composed of two nonmagnetic (NM) leads separated by a periodic spacer. The spacer is composed of one-dimensional heterostructure formed by a sequence of magnetic (A) and nonmagnetic (B) sites periodically juxtaposed (as in a typical periodic quantum dot (QD)). The calculations are based on the tight-binding model and transfer matrix method, which compute the current–voltage characteristic within the Landauer–Buttiker formalism. Our main goal is to assess the contribution of the spin-flip scattering to the transport properties of such systems. The spin-dependent transport behavior can be controlled via a gate magnetic field and an applied voltage in the ballistic regime. Our results show that the conductance strongly depends on the configurations of the magnetic QD. The application of the predicted results may be useful in designing spin-valve devices, such as spin-polarized molecular transistors.

We study the influence of shape, orientation, size and material system on the band structure of quantum wires with special attention given to the differences between results obtained with the Burt–Foreman and the Luttinger–Kohn Hamiltonians. We also show how to derive the Hamiltonians for an arbitrary orientation. We find that the difference is independent of the shape and orientation of the quantum wire, but it does depend on the size and the material system chosen. A brief discussion of the results in terms of group theory is provided.

The effect of barrier thickness on strain uniformity of a laterally aligned array of InGaAs quantum wire in GaAs matrix has been investigated with the finite elements method. A decrease in GaAs barrier thickness was predicted to assist the InGaAs wire to maintain its strain state in the central region up to a longer distance towards the edge of the wire along the width direction. It is suggested that, by reducing the spacing between the quantum wires, it is possible to improve uniformity of strains within the wire, thereby yielding more uniform opto-electronic properties such as sharp and narrow peaks in photoluminescence spectra.

A model calculation is reported for the tunneling probability of one as well as two interacting electrons from a quantum well within a narrow channel. We discuss the cases when the two electrons are spin polarized or unpolarized by transforming the system to a noninteracting one with the use of quantal density functional theory to obtain an effective single-particle confining potential. A semiclassical approach is used to obtain the tunneling probability from this effective potential. The calculation is motivated by recent measurements of the conductance of an electron gas in a narrow channel but is not meant to explain the anomalous behavior that has been reported since, for example, we deal with a simplified two-level system. Numerical results for the tunneling probability are presented.

High-quality T-shaped quantum wire lasers are fabricated by cleaved-edge overgrowth with the molecular beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal. Micro-photoluminescence (PL) and PL excitation spectroscopy reveals unprecedented high quality of the wires, and structures of one-dimensional (1D) free excitons and 1D continuum states. At high pumping levels, PL evolves from a sharp free exciton peak via a biexciton peak to a red-shifted broad band. Lasing has been achieved with low lasing threshold. The lasing energy is on the red-shifted broad band and is about 5 meV below the free exciton. The observed shift excludes free excitons in lasing, and suggests contribution of highly Coulomb-correlated electron–hole plasma.

We have carried out an explicit closed-form determination of the inverse dielectric function for a single one-dimensional (1D) quantum wire embedded in a nonlocal 3D bulk semiconductor plasma and analyzed the coupled mode plasmon dispersion relation in the hydrodynamic model. Our analysis shows that the coupled 1D-3D plasmon is damped due to even small nonlocality of the 3D plasma. Also, there is a new nonlocal low frequency mode which does not exist for either the quantum wire or the nonlocal host in the absence of the other. © 2002 Elsevier Science Ltd. All rights reserved.

We demonstrate strong one dimensional (1-D) many-body interaction effects in photoluminescence (PL) in a GaAs single quantum wire of unprecedented optical quality, where 1-D electron plasma densities are controlled via electrical gating. We observed PL of 1-D charged excitons with large binding energy of 2.3 meV relative to the neutral excitons, and its evolution to a Fermi-edge singularity at high electron density. Furthermore, we find a strong band-gap renormalization in the 1-D wire, or a large red-shift of PL with increased electron plasma density. Such a large PL red-shift is not observed when we create a high density neutral electron-hole plasma in the same wire, due probably to cancellation of the Coulomb interaction energy in the neutral plasma., 5 pages, 4 figures, RevTeX, to be published in Solid State Communications

Raman spectra of a circular quantum wire have been calculated in the presence of the electron–phonon coupling treated in the random phase approximation. It is predicted that the collective excitations (plasmons) associated with the azimuthal motion of the electrons in the sample would not only shift the position of the Raman line but, split it into two peaks. The current experimental situation is discussed.

We have studied theoretically the quantum conductance in a nanostructure with a set of antidots inside a quantum wire. The conductance is obtained using the Landauer–Buttiker formalism. Two basic configurations are considered: two antidots aligned in the longitudinal direction in the center of the quantum wire and four antidots symmetrically distributed in the wire. We find oscillation in the conductance due to the first and the second transverse subbands. The numerical results show that the position and strength of the conductance peaks can be controlled by the geometry parameters of the structures.

The spin–orbit coupling effect on the linewidth enhancement factor (LWEF) of InGaAs/InP strained quantum wire lasers is theoretically investigated using a 6×6 Luttinger–Kohn Hamiltonian. The peak gains are overestimated for both the unstrained and the compressively strained quantum wire lasers in a 4×4 Luttinger–Kohn model. The increase in the density of states also results from the spin–orbit coupling effects. For the case of the compressively strained quantum wire lasers, the spin–orbit coupling effect greatly improves the LWEF. The unstrained system has better property of the LWEF than the compressively strained one at high injection carrier density.

For the first time, the quantum free-electron theory is utilized for determining the quantized electrical conductance in a perfect metallic multi-atom nanowire. In this formulation, both spin-up and spin-down conduction electrons are considered so that our final result comes from a series combination of the contributions to the conductance from the two possible types of spin-oriented electron, assuming a symmetric distribution of the involved counter-ions. In addition, several aspects related to the atom-lead coupling are discussed.

We show that the optical absorption and emission energies in porous silicon can be accounted for in a quantum wire confinement model where both the electron and the hole are localized by lateral surface wire undulations. Localization energies for both the particles have been numerically calculated within the effective mass approximation showing that there exists a limited class of wire geometries which are consistent with porous silicon optical and structure analysis data.

We have studied the recombination mechanism of InGaAs/GaAs V-shaped quantum wire lasers under electrical injection and in high magnetic field, from well below to above lasing threshold. The emission originates from free-carrier recombination independent of temperature and injection density. No excitonic contribution is found, indicating that excitons are weakly bound in these wires due to the internal piezoelectric field causing a strong Stark effect. A quantitative analysis of the piezoelectric field is performed by measuring the screening induced blue-shift of the electroluminescence at different densities and comparing it with the piezoelectric potential calculated from the quantum wire cross-sections observed by transmission electron microscopy. (C) 1999 Elsevier Science Ltd. All rights reserved.

The effects of spin–orbit split-off band on InGaAs/InP strained quantum wire structures are theoretically investigated using 6×6 Luttinger–Kohn Hamiltonian. The strong coupling of spin–orbit split-off band with other states has considerable effects on optical properties. It shows that the peak gains are underestimated for the unstrained and the tensile strained quantum wires in 4×4 Luttinger–Kohn model. The change of the density of states and the dipole moments are the main factors for the inconsistent results between the 4×4 and the 6×6 models in the linear optical gain. In the tensile and the unstrained quantum wire structures, the threshold carrier densities are reduced by spin–orbit coupling. The compressive strained structure has the lowest threshold carrier density and the highest differential gain. As a whole, the differential gain is improved by the spin–orbit coupling effects.

We calculate the ground-state energy of an interacting quasi-one-dimensional electron gas depending on the spin-polarization parameter ζ . For a quantum wire with a width parameter β we calculate the spin-susceptibility κ s as a function of β and the Wigner-Seitz parameter r s . We derive analytical results for κ s within the Hartree-Fock approximation and the mean-spherical approximation. The numerical results obtained for the spin-susceptibility are fitted by an analytical expression.

We calculate the electronic resistivity of a GaAs-based semiconductor quantum wire in the presence of acoustic phonon scattering. We find that the usual Drude-Boltzmann transport theory leads to a low temperature activated behavior instead of the well-known Bloch-Gr\"uneisen power law. Many-body electron-phonon renormalization, which is entirely negligible in higher dimensional systems, has a dramatic effect on the low temperature quantum wire transport properties as it qualitatively modifies the temperature dependence of the resistivity from the exponentially activated behavior to an approximate power law behavior at sufficiently low temperatures., Comment: 11 pages, RevTex, 4 figures. Also available at http://www-cmg.physics.umd.edu/~lzheng/preprint/

The polarizability and the ground state binding energy of a donor impurity located in a semiconductor quantum well wire of rectangular cross-section with finite barrier potential is calculated through the variational method. We assume that the donor is located at the center of the wire and that the electric field is applied in the direction perpendicular to the wire length ( z -direction), making an angle θ with the x -axis. We present our results for the ground state binding energy as a function of the size of the wire for several values of the electric field strength and of the angle θ. It is found that the polarizabilities decrease as the wire dimensions ( L x and L y ) decrease, until they reach a minimum at a certain value of L x ( L y fixed) and then increase as the width becomes smaller. The binding energies and the polarizabilities, as expected, have a strong dependence on the geometrical form of the wire and on the angle θ.

Theoretical predictions of polaron effects on the third-harmonic generation in a rectangular quantum wire with an additional parabolic potential are presented. The formula for the third-harmonic generation along the wire is derived by density matrix method. The numerical results are presented for a typical GaAs quantum wire.

The linear response conductance is computed in a one-dimensional atomic wire between two adiabatically expanding metal electrodes. We show that the conductance behavior is significantly different from that of a mesoscopic narrow channel. Specifically, we find that the conductance of such an atomic wire oscillates periodically between quantum unit of conductance G Q for odd number of atoms in the wire and rG Q ( r

A theoretical investigation on how the band structure of bulk semiconductors specifically affects the quantum confinement in quantum dots is presented, using Ge as an example. The intrinsic difference of the quantum confinement of different symmetrical valence states may bring some completely new physics as the quantum dot size decreases.

One-dimensional structures are expected to show unique electronic transport behavior as a consequence of the Coulomb interaction between carriers. A considerable number of theoretical predictions remain largely untested by experiment due to a lack of a suitable one-dimensional wire. Using a new crystal growth technique a unique tube-like structure with a cross section of 25 nm × 25 nm has been created in a semiconductor. The mean free path of the electrons exceeds 10 μm - more than 400 times the confinement dimension. The energy spacing between one-dimensional modes far exceed any random potential fluctuations and is more than 10 times larger than previously achieved by other techniques. The conductance plateaus of these wires deviate significantly from the expected universal values suggesting the relevance of electron-electron interactions.

We calculate the exchange energy, the correlation energy and the compressibility for a quantum wire using a three-sum-rule approach for the local-field correction. An anisotropic confinement model with δ-confinement in one direction and an oscillator confinement in the other direction is used in the calculation. We perform a systematic study versus the electron density and the width parameter of the wire and we present analytical and numerical results. In the low density regime the inverse compressibility is strongly negative and this might be observable via capacitance measurements. We predict a spin instability at low density, depending on the confinement parameter.

Cataloged from PDF version of article. We present a fully dynamical and finite temperature study of the hot-electron momentum relaxation rate and the power loss in a coupled system of electron-hole plasma and bulk LO-phonons in a quantum wire structure. Interactions of the scattered electron with neutral plasma components and phonons are treated on an equal footing within the random-phase approximation. Coupled mode effects substantially change the transport properties of the system at low temperatures. Particularly, the ''plasmon-like'' and ''LO-phonon-like'' excitations yield comparable rates which, as a consequence of the singular nature of the 1D density of states, can be large at the threshold. This is in contrast to room temperature results where only the LO-phonon mode contributes significantly to the rate. The density and temperature dependence of the power loss reveals that dynamical screening effects are important, and energy-momentum conservation cannot be satisfied above a certain density for a given initial energy. Copyright (C) 1996 Elsevier Science Ltd

We report theoretical studies of electron transport in a quantum wire containing double-paralleled or double-series slits and a “detector” slit. Strong conductance oscillations due to quantum interference are produced in both structures when the position of a detector slit in the quantum wire is changed. We interpret these interference effects in terms of multiple reflections of a phase-coherent electron along the quantum wire and circulating-bound-states in a resonant-box region. We also examine the transmission coefficients and electronic phase shifts which provide insights into the origins of conductance oscillations. For the double-paralleled system, the dependence of the interference effects on the slit width and the detector distance is discussed.

The exact wave functions for a strictly parabolic quantum wire with applied electric fields are given. Considering the anharmonic perturbing potential we derive in this paper the analytical expressions for nonlinear polarization using the density matrix formalism. We discuss the nonlinear optical effects of different orders in detail and also give a numerical illustration.

We have studied the resonance patterns on the Hall and the nonlocal resistances in an H shaped quantum wire conductor with and without a magnetic field. We have found that the resonance patterns on the Hall resistance can be explained by usual multiple reflections of electron waves in a bridge-like portion of the H structure. However, we have found that the resonance patterns on the nonlocal resistance are mainly caused by inter-mode transitions of two highest modes in the system, which yield large oscillations in a mixing frequency in the resistance curve with respect to all the physical variables we have considered, such as the Fermi energy and the magnetic field. Due to largeness of the period of the nonlocal oscillations, we propose that the nonlocal resistance is a better candidate for observation of resonance in real experimental settings.

A technique utilizing changes in the conductance of a quantum wire to measure the detrapping time and density of electron traps is described. The technique permits the study of defects in heterostructure material over a wide range of doping levels and under a variety of conditions. The technique also introduces the possibility of studying one microsecond or faster (de)trapping times.

We report on approximate energy levels calculations in semiconductor quantum wires using separable wavefunctions. These are the solutions of the Hartree-like integro-differential equations for two one-dimensional carriers which interact through the bi-dimensional confining potential of the wire. Surface quantum wires and T-shaped wires are used as examples.

We calculate the rate for scattering of electrons with acoustical phonons for the lowest subband of a quantum wire in a magnetic field. It is shown that this rate exhibits a crossover behavior when the Fermi velocity υF becomes larger than the speed of sound cS. For υF cS. The latter should result in a corresponding reduction of the conductance plateaus in quantum wires with increasing temperature.

Considering the interaction of the electron with surface-optical (SO) phonons in polar crystals, we have studied the cyclotron resonance of magnetopolaron in cylindrical quantum wires. The results show that, with the increasing radius of the quantum wire, both the electron-SO phonon interaction energy and the cyclotron resonance frequency decrease mononically. For the same radius of quantum wire, the cyclotron resonance frequency increases almost linearly with the applied magnetic field in the weak magnetic field limit.