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Electronic structures and magnetic properties of various possible ternary transition-metal compounds based on zincblende ZnTe and CdTe semiconductors are systematically explored by using an accurate density-functional method. Half-metallic (HM) ferromagnetism is found in the ZnTe and CdTe heavily doped with Cr, V, and Mn. Quite high Curie temperatures would be expected in most of these HM ferromagnets. These HM ferromagnetic phases, structurally stable and compatible with the two semiconductors, would be useful in spintronics. [ABSTRACT FROM AUTHOR]

Rutile CrO2 is the most important half-metallic material with nearly 100% spin polarization at the Fermi level, and rutile TiO2 is a wide-gap semiconductor with many applications. Here, we show through first-principles investigation that a single-unit-cell CrO2 layer on rutile TiO2 (001) surface is ferromagnetic and semiconductive with a gap of 0.54 eV, and its electronic state transits abruptly to a typical metallic state when an electrical field is applied. Consequently, this makes an interesting electrical switching effect which may be useful in designing spintronic devices. [ABSTRACT FROM AUTHOR]

Periodically driven systems can host many interesting phenomena. Two-dimensional Dirac systems irradiated by circularly polarized light are especially attractive thanks to the special absorption and emission of photons near Dirac cones. Here, letting the light travel in the two-dimensional plane, we treat the light-driven Dirac systems by using a unitary transformation, instead of usual Floquet theory, to capture the photon-mediated electronic correlation effects. In this approach, the direct electron–photon interaction terms can be removed and the resulting effective electron–electron interactions can produce important effects. The effective interactions can produce topological band structure in the case of irradiated 2D Dirac fermion system, and can lift the energy degeneracy of the Dirac cones for irradiated graphene. This method can be applied to other light-driven Dirac systems to investigate their photon-mediated electronic effects. These phenomena would be observed with ultraviolet light in some effective two-dimensional Dirac systems of honeycomb long-period superstructures. [ABSTRACT FROM AUTHOR]

Excellent monolayer electrode materials can be used to design high-performance alkali-metal-ion batteries. Here, we propose two-dimensional ReN2 monolayers as superior sodium-ion battery materials. Our total energy optimization results in a buckled tetragonal structure for the ReN2 monolayer, and our phonon spectrum and elastic moduli prove that it is dynamically and mechanically stable. Further investigations show that it is metallic and still keeps its metallic feature after the adsorption of Na or K atoms, and the adsorption of Na (or K) atoms changes the lattice parameters by 3.2% (or 3.8%) at most. Its maximum capacity reaches 751 mA h g−1 for Na-ion batteries or 250 mA h g−1 for K-ion batteries, and the diffusion barrier is only 0.027 eV for the Na atom or 0.127 eV for the K atom. The small lattice changes, high storage capacity, metallic feature, and extremely low ion diffusion barriers make the ReN2 monolayers a superior electrode material for Na-ion rechargeable batteries with ultrafast charging/discharging processes. [ABSTRACT FROM AUTHOR]

Fast quantum spin manipulation is needed to design spin-based quantum logic gates and other quantum applications. Here, we construct the exact evolution operator of the nitrogen-vacancy-center (NV) spin in diamond under external magnetic fields, and investigate the nonadiabatic geometric phases—both cyclic and non-cyclic—in these fast-manipulated NV spin systems. It is believed that the nonadiabatic geometric phases can be measured in future experiments, and that these fast quantum manipulations can be useful in designing spin-based quantum applications. [ABSTRACT FROM AUTHOR]

Since the advent of graphene, two-dimensional (2D) materials have become very attractive and there is growing interest in exploring new 2D materials beyond graphene. Here, through density-functional theory (DFT) calculations, we predict 2D wide-band-gap II–V semiconductor materials of M3X2 (M = Zn, Cd and X = N, P, As) with a dilated graphene-like honeycomb structure. In this structure the group-V X atoms form two X-atomic planes symmetrically astride the centering group-IIB M atomic plane. Our DFT calculation shows that 2D Zn3N2, Zn3P2 and Zn3As2 have direct band gaps of 2.87, 3.81 and 3.55 eV, respectively, and 2D Cd3N2, Cd3P2 and Cd3As2 exhibit indirect band gaps of 2.74, 3.51 and 3.29 eV, respectively. Each of the six 2D materials is shown to have effective carrier (either hole or electron) masses down to 0.03m0–0.05m0. The structural stability and feasibility of experimental realization of these 2D materials has been shown in terms of DFT phonon spectra and total energy comparison with related existing bulk materials. On the experimental side, there already are many similar two-coordinate structures of Zn and other transition metals in various organic materials. Therefore, these 2D semiconductors can enrich the family of 2D electronic materials and may have promising potential for achieving novel transistors and optoelectronic devices. [ABSTRACT FROM AUTHOR]

The electronic structures, the effective masses, and optical properties of spinel CdCr2S4 are studied by using the full-potential linearized augmented planewave method and a modified Becke–Johnson exchange functional within the density-functional theory. Most importantly, the effects of the spin–orbit coupling (SOC) on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center. SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr2S4. These should be useful to deeply understand spinel CdCr2S4 as a ferromagnetic semiconductor for possible semiconductor spintronic applications. [ABSTRACT FROM AUTHOR]

It has been proposed that antiferromagnetic Fe adatom spins on semiconductor Cu–N surfaces can be used to store information (Loth et al 2012 Science335 196). Here, we investigate spin dynamics of such antiferromagnetic systems through Monte Carlo simulations. We find out the temperature and size laws of switching rates of Néel states and show that the Néel states can become stable enough for the information storage when the number of spins reaches one or two dozens of the Fe spins. We also explore promising methods for manipulating the Néel states. These could help realize information storage with such antiferromagnetic spin systems. [ABSTRACT FROM AUTHOR]