We investigate the spin-dependent electric and thermoelectric properties of ferromagnetic zigzag α-graphyne nanoribbons (ZαGNRs) using density-functional theory combined with non-equilibrium Green's function method. A giant magnetoresistance is obtained in the pristine even-width ZαGNRs and can be as high as 10⁶%. However, for the doped systems, a large magnetoresistance behavior may appear in the odd-width ZαGNRs rather than the even-width ones. This suggests that the magnetoresistance can be manipulated in a wide range by the dopants on the edges of ZαGNRs. Another interesting phenomenon is that in the B- and N-doped even-width ZαGNRs the spin Seebeck coefficient is always larger than the charge Seebeck coefficient, and a pure-spin-current thermospin device can be achieved at specific temperatures.

Based on nonequilibrium Green's functions (NGF) and density-functional theory (DFT), we investigate the magnetotransport properties and magnetothermoelectric effects in zigzag graphene nanoribbons (ZGNRs) with non-magnetic doping on the double ribbon edges. One of the carbon atoms without hydrogen saturation in each ribbon edge is replaced by one boron (B) or one nitrogen (N) atom. Compared with boron–boron (BB) and nitrogen–nitrogen (NN) double-edge doping, the boron–nitrogen (BN) double-edge doping induces a perfect spin-filter effect with 100% negative spin polarization at the Fermi level. Moreover, we find that the thermoelectric effect can be enhanced by the double-edge doping. Interestingly, the spin Seebeck effect in NN- and BN-doped ZGNRs becomes comparable with the charge Seebeck effect and even larger than it. These results originate from the spin-dependent transmission node near the Fermi level induced by the non-magnetic doping. These findings strongly suggest that the double-edge-doped ZGNRs are promising materials for spintronics and thermo-spintronics.

We have investigated the Coulomb screening properties and plasmon spectrum in a bilayer graphene under a perpendicular electric bias. The bias voltage applied between the two graphene layers opens a gap in the single-particle energy spectrum and modifies the many-body correlations and collective excitations. The energy gap can soften the plasmon modes and lead to a crossover of the plasmons from a Landau damped mode to being undamped. Plasmon modes of long lifetime may be observable in experiments and may have potentials for device applications.

We demonstrate that giant current and high spin rectification ratios can be achieved in atomic carbon chain devices connected between two symmetric ferromagnetic zigzag-graphene-nanoribbon electrodes. The spin dependent transport simulation is carried out by density functional theory combined with the non-equilibrium Green's function method. It is found that the transverse symmetries of the electronic wave functions in the nanoribbons and the carbon chain are critical to the spin transport modes. In the parallel magnetization configuration of two electrodes, pure spin current is observed in both linear and nonlinear regions. However, in the antiparallel configuration, the spin-up (down) current is prohibited under the positive (negative) voltage bias, which results in a spin rectification ratio of order 10⁴. When edge carbon atoms are substituted with boron atoms to suppress the edge magnetization in one of the electrodes, we obtain a diode with current rectification ratio over 10⁶.

We report a first-principles study of the magnetic properties and spin caloritronics of zigzag-type blue phosphorene nanoribbons (zBPNRs). It is found that the bare zBPNR (0H-zBPNR) or monohydrogenated zBPNR (1H-zBPNR) exhibit spin-semiconducting properties arising from the edge electronic states. We further confirm that the p_y orbitals of the edge P atoms have the main contributions to these states. The spin-semiconducting property has a natural advantage for fabricating perfect thermospin devices with a stronger spin Seebeck effect than charge Seebeck effect at the Fermi level. When a temperature difference is applied, the electric current with the different spin index displays a bipolar behavior, and the spin-filtering efficiency can reach 1200%. By changing the widths of 0H-zBPNR and 1H-zBPNR, the ratio of the spin Seebeck coefficient to the charge Seebeck coefficient at the Fermi level is about 10 at room temperature.

The electronic structure and conductance of substitutionally edge-doped zigzag silicene nanoribbons (ZSiNRs) are investigated using the nonequilibrium Green's function method combined with the density functional theory. Two-probe systems of ZSiNRs in both ferromagnetic and antiferromagnetic states are considered. Doping effects of elements from groups III and V, in a parallel or antiparallel magnetic configuration of the two electrodes, are discussed. By switching on and off the external magnetic field, we may convert the metallic ferromagnetic ZSiNRs into insulating antiferromagnetic ZSiNRs. In the ferromagnetic state, even- or odd-width ZSiNRs exhibit a drastically different magnetoresistance. In an odd-width edge-doped ZSiNR a large magnetoresistance occurs compared to that in a pristine ZSiNR. The situation is reversed in even-width ZSiNRs. These phenomena result from the drastic change in the conductance in the antiparallel configuration.