摘要 :
Multishell helical gold nanowires (HGNs) suspended between semi-infinite electrodes are found to exhibit peculiar electron-conduction properties by first-principles calculations based on the density functional theory. Our results ...
展开
Multishell helical gold nanowires (HGNs) suspended between semi-infinite electrodes are found to exhibit peculiar electron-conduction properties by first-principles calculations based on the density functional theory. Our results that the numbers of conduction channels in the HGNs and their conductances are smaller than those expected from a single-atom row nanowire verify the recent experiment. In addition, we obtained a more striking result that, in the cases of thin HGNs, distinct magnetic fields are induced by the electronic current helically flowing around the shells. This finding indicates that the HGNs can be good candidates for nanometer-scale solenoids.
收起
摘要 :
We have theoretically studied the optical absorption coefficient of quantum wires in electric and strain fields with intermixing interfaces. The potential profiles are governed by the intermixing heterojunctions, internal strain d...
展开
We have theoretically studied the optical absorption coefficient of quantum wires in electric and strain fields with intermixing interfaces. The potential profiles are governed by the intermixing heterojunctions, internal strain due to the lattice mismatch, the external electric field and stress. The second Fick's law describes the wires' intermixing heterojunctions due to the alloy interdiffusion. We adopt the Green's function method to solve the Poisson equation for the displacement to determine the internal strain due to the lattice mismatch. The single-band Schroedinger equation in the effective mass approximation is used to describe the conduction subband structures while the four-band Kohn-Luttinger Hamiltonian is used to describe the valence subband structures. In solving the Schroedinger equation and the Kohn-Luttinger Hamiltonian, we expand the wave functions for the electrons and holes by using linear combinations of the two-dimensional harmonic oscillator wave functions to yield two matrix equations. These matrix equations are numerically solved for their eigen-energies and their corresponding eigenfunctions. We investigate some physical properties of the unstrained quantum wire (GaAs/AlAs) and the strained wire (CdSe/ZnSe) as examples. When the interdiffusion becomes stronger, on one hand, the internal strain is relaxed leading to the band gap shrinkage (if the initial strain ε_0 < 0) and, on the other hand, the potential profiles are deformed and the effective band gap becomes wider. Variations of the transition energies with external stress show the anticrossing effect and variations of the transition energies with external electric field show the field emission effect. The hole effective masses can be enhanced or become electronlike by applying stress to the wire. The oscillator strengths of the dipole-allowed intersubband transitions for the y and z polarizations are calculated to infer possible optical transitions. The optical absorption coefficients together with the joint density of states are calculated.
收起
摘要 :
We study an electron transport property in two parallel quantum wires with random potentials. Assuming the same microscopic parameters for both wires, we focus on the relationship between interwire interaction and electron backwar...
展开
We study an electron transport property in two parallel quantum wires with random potentials. Assuming the same microscopic parameters for both wires, we focus on the relationship between interwire interaction and electron backward scattering by random potentials at low energy regime. Our analytical and numerical calculations show that the Drude weight, a measure of the electron transport, is influenced by interwire interaction and random potential independently, and little coupling between those two is observed, which is in contrast to a deep relationship between up- and down-spin interactions and random potentials in a single wire. It leads to that interwire interactions do not have a great influence on the Anderson localization in each wire.
收起
摘要 :
We present the first-principles study of the coherent relationship between the optimized geometry and conductance of a three-aluminum-atom wire during its elongation. Our simulation employs the optimum model including semi-infinit...
展开
We present the first-principles study of the coherent relationship between the optimized geometry and conductance of a three-aluminum-atom wire during its elongation. Our simulation employs the optimum model including semi-infinite crystalline electrodes using the overbridging boundary-matching method [Phys. Rev. B 67, 195315 (2003)] extended to incorporate nonlocal pseudopotentials. The results that the conductance of the wire is ～ 1 G_0 and that the conductance trace as a function of electrode spacing shows a convex downward curve before breaking are in agreement with experimental data.
收起
摘要 :
We present a first-principles study of the electron conduction properties of single-row nanowires suspended between semi-infinite electrodes. The single-row sodium nanowires exhibit conductance oscillation and bunching of high ele...
展开
We present a first-principles study of the electron conduction properties of single-row nanowires suspended between semi-infinite electrodes. The single-row sodium nanowires exhibit conductance oscillation and bunching of high electron density with two atom lengths in the channel density distribution. The relationship between the period of the conductance oscillation and the length of the bunches is interpreted using a simplified model. The difference in the penetration parameters between the incident Bloch, wave and the reflected one inside the nanowire is closely related to the period of the conductance oscillation and the length of the bunches.
收起
摘要 :
We report on the theoretical investigation of magnetoplasmon excitations in a quantum wire characterized by a confining harmonic potential and in the presence of a perpendicular magnetic field. The problem involves two length scal...
展开
We report on the theoretical investigation of magnetoplasmon excitations in a quantum wire characterized by a confining harmonic potential and in the presence of a perpendicular magnetic field. The problem involves two length scales: I_0=(h/m~*ω_0)~(1/2) and l_c=I_0=(h/m~*ω_c)~(1/2), which characterize the relative strengths in the interplay of confinement and the magnetic field. We embark on the charge-density excitations within a two-sub-band model in the framework of Bohm-Pines' random-phase approximation. The main focus of our study is the (inter-sub-band) magnetoroton excitation which changes the sign of its group velocity twice before merging with the respective single-particle continuum. We analyze the terms and conditions within which the magnetoroton excitation persists in the quantum wires. It is suggested that the electronic device based on such magnetoroton modes can act as an active laser medium.
收起
摘要 :
We investigate the transmission of electrons between conducting nanoribbon leads oriented at multiples of 60° with respect to one another, connected either directly or through graphene polygons. A mode-matching analysis suggests ...
展开
We investigate the transmission of electrons between conducting nanoribbon leads oriented at multiples of 60° with respect to one another, connected either directly or through graphene polygons. A mode-matching analysis suggests that the transmission at low energies is sensitive to the precise way in which the ribbons are joined. Most strikingly, we find that armchair leads forming 120° angles can support either a large transmission or a highly suppressed transmission, depending on the specific geometry. Tight-binding calculations demonstrate the effects in detail and are also used to study transmission at higher energies as well as for zigzag ribbon leads.
收起
摘要 :
The envelope function method is applied to hole and exciton states in wurtzite and zinc-blende structure cylindrical nanowires using the axial Kohn-Luttinger Hamiltonian including a crystal-field splitting for the wurtzite case. T...
展开
The envelope function method is applied to hole and exciton states in wurtzite and zinc-blende structure cylindrical nanowires using the axial Kohn-Luttinger Hamiltonian including a crystal-field splitting for the wurtzite case. The quantized states are found to be mixtures of heavy- and light-hole band derived states. Explicit expressions for the mixing coefficients and the conditions giving the quantized energy states are derived. These are then applied to obtain the relative intensity of light emitted polarized parallel and perpendicular to the nanowire for the lowest-energy excitons. Slightly different expressions are obtained in the weak quantization and strong quantization limits. In the latter case, an overlap integral of the hole and electron envelope function is involved, while in the former case only an integral over the hole envelope function is required. An expression for the degree of polarization of the spectrally integrated photoluminescence as a function of temperature is obtained by summing over the excitons within the integration range. The degree of polarization as a function of temperature is explored numerically as a function of nanowire radius and crystal-field splitting for GaAs and GaN nanowires. Examples of complete reversal of the polarization are illustrated.
收起
摘要 :
We have studied the ground state structure of quantum strips within the local spin-density approximation, for a range of electronic densities between ～5 X 10~4 and 2 X 10~6cm~(-1) and several strengths of the lateral confining po...
展开
We have studied the ground state structure of quantum strips within the local spin-density approximation, for a range of electronic densities between ～5 X 10~4 and 2 X 10~6cm~(-1) and several strengths of the lateral confining potential. The results have been used to address the conductance G of quantum strips. At low density, when only one subband is occupied, the system is fully polarized and G takes a value close to 0.7(2e~2/h), decreasing with increasing electron density in agreement with experiments. At higher densities the system becomes paramagnetic and G takes a value near (2e~2/h), showing a similar decreasing behavior with increasing electron density. In both cases, the physical parameter that determines the value of the conductance is the ratio K/K_0 of the compressibility of the system to the free one.
收起
摘要 :
We present a study of the optical absorption spectra of thin silicon nanowires using many-body perturbation theory. We solve the Bethe-Salpeter equation in the static approximation using a technique that avoids explicit calculatio...
展开
We present a study of the optical absorption spectra of thin silicon nanowires using many-body perturbation theory. We solve the Bethe-Salpeter equation in the static approximation using a technique that avoids explicit calculation of empty electronic states, as well as storage and inversion of the dielectric matrix. We provide a detailed assessment of the numerical accuracy of this technique, when using plane wave basis sets and periodically repeated supercells. Our calculations show that establishing numerical error bars of computed spectra is critical, in order to draw meaningful comparisons with experiments and between results obtained within different algorithms. We also discuss the influence of surface structure on the absorption spectra of nanowires with ≌1-nm diameter. Finally, we compare our calculations with those obtained within time-dependent density functional theory and find substantial differences, more pronounced than in the case of Si nanoparticles with the same diameter.
收起
