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Electronic transport through a parallel coupled multiple triple-quantum-dots (tQDs) chain is theoretical studied. By producing an energy difference between the site energy of the upper QDs and the down ones and considering a Zeeman splitting, several highly to 100% spin-polarized windows (SPWs) with very steep edges appear in the linear conductance spectra due to the Fano antiresonance. Moreover, if the Dicke resonance is considered, some nearest SPWs with opposite direction of the spin polarization just contact with each other in some suitable conditions. These results strongly support that this multi-tQDs device can serve multiple purposes including perfect spin-filtering and quantum-signal generator. [ABSTRACT FROM AUTHOR]

Motivated by the experimental synthesis of bulk MnTe with rocksalt structure, we use the first-principles calculations to explore the structural, electronic, and magnetic properties of VTe in four different phases: rocksalt, zinc-blende, wurtzite, and ground-state NiAs. It is found that the ground-state NiAs phase is antiferromagnetic, but both the zinc-blende and wurtzite phases exhibit truly half-metallic ferromagnetism, and the rocksalt phase is a nearly half-metal. Importantly, the rocksalt phase is energetically more stable than the zinc-blende and wurtzite ones. We further reveal that there is an interesting transition from the nearly half-metallicity in bulk rocksalt VTe to the truly half-metallicity at the Te-terminated (111) surface, and the Te-terminated (111) surface is energetically more stable than the V-terminated (111) surface, which makes VTe with rocksalt structure promising candidate for spintronic applications. [ABSTRACT FROM AUTHOR]

Charge and spin-polarized transport through a parallel coupled triple-quantum-dot (tQD) device with common source and drain electrodes has been theoretically investigated by means of the nonequilibrium Green's function formalism. By introducing a local Rashba spin-orbit interaction on a QD and considering an Aharonov-Bohm flux through the tQD ring, we find that there is a spin-polarized current (Is) occurring and oscillating in its current-voltage curves. The direction of the spin polarization can be inverted frequently by altering applied bias voltage (V), which turns to result in a multiple negative differential resistance feature in the relationship of (Is-V). Interestingly, a new type of blockade effect, i.e., spin-orbit blockade, different from the Coulomb blockade detected before, has been observed in the charge and spin-polarized currents through the tQD device. Through adjusting these two blockade effects, the tQD device can be designed and applied in the area of spin-current rectifiers and multiple-value logical devices with desirable spin-transport properties. [ABSTRACT FROM AUTHOR]

Recent studies by Gao et al. [Phys. Rev. B 75, 174442 (2007)] indicate zinc-blende CaC, SrC, and BaC exhibit robust sp half-metallic ferromagnetism with Curie temperatures higher than room temperature. Here we further investigate the surface electronic and magnetic properties of CaC by using the first-principles full-potential linearized augmented plane-wave method. The (001) surfaces terminated with Ca and C, respectively, and the (110) surface terminated with both Ca and C are considered. We discuss the surface stabilities from the calculated relaxed surface energies. Electronic structure calculations indicate that the half-metallicity is destroyed for both the Ca- and C-terminated (001) surfaces; however, the (110) surface preserves the half-metallic characteristic of the bulk CaC. We further reveal that the atomic magnetic moments of the (001) surfaces are greatly different from the bulk values, but the difference of atomic magnetic moments between the (110) surface and the bulk CaC is very small. [ABSTRACT FROM AUTHOR]

We investigate the electronic properties of one-dimensional metal-C6H6 multidecker complexes: chromium(Cr)-benzene(Bz), benzene(Bz)-chromium(Cr)-benzene(Bz)-iron(Fe) wires and CrnBz2 (n = 1, 2, 3) and CrBz2Fem (m = 1, 2) clusters by applying nonequilibrium Green's functions combined with the density-functional theory. We predict that the ground state of the FeBzCrBzFe cluster is 100% spin-polarized. The density of states shows metallic for the spin-up electrons, while a semiconductor gap merges for the spin-down electrons (half-metallic). It is found that there is 92%-97% spin polarization of the electron transmission for the five sandwich molecular junctions constructed by the multilayer metal-benzene organometallic CrnBz2 (n = 1, 2, 3) and CrBz2Fem (m = 1, 2) clusters, which coupled to gold electrodes. In deed, these clusters will perform as nearly perfect spin-filters via the electron transport calculations. The current increases with the cluster length and depends on the bias and spin-up current-voltage characteristics for three kinds of sandwich molecular junctions (Bz2Cr, BzCrBzFe, and Bz2Cr3). It also shows robust negative differential resistance behavior, which is closely related with the evolution of the transmission spectrum under applied bias. [ABSTRACT FROM AUTHOR]

Motivated by the experimental synthesis of bulk rocksalt MnS, MnSe, and MnTe, we show with first-principles calculations that among all transition-metal pnictides and chalcogenides with rocksalt structure CrTe, VPo, and CrPo are truly half-metallic ferromagnets, and both VTe and CrSe exhibit nearly half-metallicity. Importantly, for these five half-metallic compounds, the rocksalt phase is energetically more stable than the zinc-blende and wurtzite ones, and the total energy differences between the rocksalt and ground-state NiAs phases are very small (0.06-0.43 eV/f.u.) and comparable with that of experimental MnTe (0.24 eV/f.u.), thus like rocksalt manganese chalcogenides, these five rocksalt half-metals would be realized in the form of bulk or at list thin films for spintronic applications. In addition, we study the (111) surface properties of rocksalt CrPo and find both Cr- and Po-terminated (111) surfaces retain the bulk half-metallicity. We also reveal that the spin-orbit coupling has very weak effect on the half-metallicity of rocksalt CrSe, VTe, and CrTe, and the spin polarizations are still high for rocksalt VPo and CrPo although the spin-orbit coupling affects greatly their half-metallicities. [ABSTRACT FROM AUTHOR]

Electronic transport through a diamondlike quantum network device composed of multiple quantum dots (QDs) is theoretically studied by means of the nonequilibrium Green's function approach. In this system, by producing an energy difference between the site energy of the upper and down QDs through adjusting the gate voltages, the linear conductance spectrum shows a valley structure with a zero point due to the occurrence of Fano antiresonance. As the energy difference increases or the network chain size increases to a not very large value, the antiresonant valleys in the conductance spectra change to well-defined insulating bands with very steep edges. Moreover, the conditions for the occurrence of the Fano antiresonance and its relation with the formation of the well-defined insulating bands are studied. By introducing a Zeeman effect due to an external magnetic field, the spin-splitting conductance spectra show several highly to 100% spin-polarized windows, which proposes that this network device can be used as a perfect spin filter and generate a completely spin-polarized current. In addition, the many-body effect due to the intradot electron-electron interaction on the profile of the insulating bands is also investigated. It is found that the main characteristics of the well-defined insulating band remain and the highly spin-polarized window splits into several sub-ones still possessing the very steep edges, indicating that the many-body effect does not affect its application for a perfect spin filter. [ABSTRACT FROM AUTHOR]