A three-terminal spin filter induced by spin-orbit interaction in the presence of an antidot Three-terminal devices have been frequently proposed to generate the pure spin current. However, the controllability and stability of pure spin current still needs to be improved. In this paper, a three-terminal device, composed of a ferromagnetic metallic lead and two nonmagnetic semiconductor leads coupled with a quantum dot, is employed to study the properties of electron spin transport. The results show that when the external voltage on one of nonmagnetic semiconductor leads is adjusted to a proper range, a pure spin current plateau or a fully spin-polarized current plateau appears in another nonmagnetic semiconductor lead. In a wide range of external voltage, the pure spin current or the spin-polarized current is kept unchanged. Since the change of temperature may considerably influence the spin-polarization of current and is inevitable actually, we studied the corresponding compensation to keep the pure spin current unchanged. Furthermore, the effect of device parameters on the pure spin current is also investigated. V C 2014 AIP Publishing LLC.

The Schrödinger equation for a particle in the V-shaped potential decorated by a repulsive or attractive Dirac delta function interaction at the center is solved, demonstrating the crucial influence of point interaction on the even-parity states of the original system without decoration. As strength of the attraction increases, the ground state energy falls down without limit; and in limit of infinitely large attraction, the ground state approaches a singular state. Our analysis and conclusion can be readily generalized to any one-dimensional system a particle interacts with symmetrical potential plus the Dirac delta function interaction at the center.

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Plasmonic excitations in mesoscopic-sized atomic chains are investigated by employing the tight-binding model. Based on the quantum response theory and random phase approximation, a plasma oscillation eigen-frequency equation is derived for calculation of the plasmon energy spectrum. The plasmon energy spectrum has been numerically calculated, and the eigen-oscillation of the system and the resonance behavior under the external electric field applied on the atom chain are investigated, respectively. Dependence of plasmonic excitation energy on the length of systems and electron density has been discussed. Results suggest that in the case of resonance, the resonant peak of dipole moment is corresponding to the plasmonic excitation, and this indicates that the external electric field excites the plasmon of the system. In resonance the oscillation amplitude of the charge is much larger than that in the case of non-resonance, especially the imaginary part of the charge has a more obvious enhancement. For the eigen-oscillations, the plasmonic excitation energy is greater than the single-particle excitation state at the same level; the length of atomic chains, the electron density, and the strength of Coulomb correlation have significant effects on the plasmon spectroscopy. For the given atom-chain length, with variation of number of electrons, the plasmonic excitation energy varies symmetrically around the half-filling. This indicates that the plasmon spectrum of the system is symmetrical for the electrons and holes.

Plasmon in quantum dot system is one of the most notable research topics in the field of optoelectronics. With the development of nanotechnology, plasmon in nano-structure has received considerable attention due to its potential applications in future natural science areas. To better understand the quantum effect and the properties of plasmon, in this paper we use the linear response theory and the tight-binding approximation to investigate the collective response of charge in a twodimensional square quantum dot system. The results show that when the frequency of the external field equals the frequency of the plasmon, there are strong charge collective oscillations in the quantum dot system, accompanied by great energy absorption and near-field enhancement. Owing to the quantization of plasmon, the collective charge oscillations in a two-dimensional square quantum dot system are found at different frequencies. The number of quantum modes of plasmon increases with the size and electron number of square quantum dots increasing, this behaviour of quantum mode of plasmon is similar to the one of phonon. The reasons for this behaviour are as follows. First, with the increase of quantum dot size, there are more energy levels around the fermi energy, and the electrons can jump from more energy levels to the outside of fermi circle, so there are more collective excitation frequencies (i.e., more quantum modes of plasmon) in a larger size system. Second, with the increase of electron number in quantum dots, there are more energy levels occupied by electrons, so there are more quantum modes of plasmon too. Furthermore, the size dependence of plasmon shows that with the increase of quantum dot size, the frequency interval between two neighbouring modes of plasmon is smaller, and the discrete modes of plasmon will gradually display quasi-continuous characteristic and transform gradually into the classical continuous modes of plasmon, and the frequency spectrum of plasmon turns into the classical dispersion relation. Such a characteristic is in accord with Bohr's correspondence principle, implying that the quantum plasmon and classical plasmon are gradually unified in a macroscopic size. The dependence of plasmon on the size and electron number of quantum dots also show that with the increase of the quantum dot size, the frequencies of the plasmon is red-shifted and the excitation intensity of the plasmon increases; with the increase of the electron number in quantum dot, the frequency of the plasmon is blue-shifted and the excitation intensity of the plasmon increases.