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Magnetic Multi-Valued (MMV) recording process is studied by numerical simulation including thermomagnetic effect. A medium, which consists of PtCo capping layer coupled to TbFeCo recording layer, switches the signal of Kerr rotation angle responding to the external field in four levels. The time evolution of generated pattern of recording mark is calculated by extending the previous magneto-optical (MO) recording simulation for single layer system.

The electron transport properties with the relativistic intrinsic and Rashba spin-orbit (SO) couplings in a graphene nanoribbon are investigated by using the third-nearest-neighbor tight-binding model and the nonequilibrium Green function method. The numerical results display a perfect quantum spin Hall state (QSH) surrounded by a simple insulator state, presented in Rashba SO coupling vs sublattice potential plane. The QSH state is enhanced by the intrinsic SO coupling, indicating a quantum topological property of graphene nanoribbons. [ABSTRACT FROM AUTHOR]

We discover a method of opening the conductive channels of zigzag graphene nanoribbons (ZGNRs) by using hydrogenation chains to separate the nanoribbon into two strips with a ∼0.7 Å distance, although the overall hydrogenation on graphene transforms the highly conductive semimetal sheet into an insulator. Two edge-like states emerge around each hydrogenation chain. The conductance enhancement, made by the hydrogenation chain, is found in nanoribbons with 5 to 7 chains, e.g. 5ZGNRH, 6ZGNRH, 7ZGNRH, and 7ZGNR2H (7ZGNR with two hydrogenation chains). The ZGNRs with hydrogenation chains illustrate their potential in nanoelectronics and carbon electronics as electronic leads and nonlinear devices. [ABSTRACT FROM AUTHOR]

We use density functional theory based nonequilibrium Green's function to self-consistently study the current through the 1,4-benzenedithiol (BDT). The elastic and inelastic tunneling properties through this Au-BDT-Au molecular junction are simulated, respectively. For the elastic tunneling case, it is found that the current through the tilted molecule can be modulated effectively by the external gate field, which is perpendicular to the phenyl ring. The gate voltage amplification comes from the modulation of the interaction between the electrodes and the molecules in the junctions. For the inelastic case, the electron tunneling scattered by the molecular vibrational modes is considered within the self-consistent Born approximation scheme, and the inelastic electron tunneling spectrum is calculated. [ABSTRACT FROM AUTHOR]

Group-IV element clathrates have attracted considerable interest in recent years. Here, we report an ab initio study on the structural stability of carbon clathrates at high pressure and identify fcc-C136 clathrate as the third most stable carbon phase after cubic diamond and hexagonal graphite. A pressure-induced phase transition is predicted to occur around 17 GPa from hexagonal graphite to fcc-C136, which is more stable than other carbon clathrates such as hex-C40 and sc-C46, and the recently predicted metastable M-carbon up to 26 GPa. Phonon dispersion calculations confirm the dynamic stability of fcc-C136 as well as diamond. [ABSTRACT FROM AUTHOR]

New magnetic configurations in 2D and 3D artificial lattices are studied by solving the non-linear equation based on the classical Heisenberg models for 2D and 3D artificial lattices. The results indicate strong possibility to be used as an ultra-high density magnetic recording media achieved by magnetic multi-valued (MMV) recording. The MMV states are based on the magnetic anisotropic configurations in 2D and 3D artificial lattices. In this paper, the magnetic properties of these artificial lattices and the density of MMV recording are discussed.

The structure and vibrational properties of high- and low-density amorphous (HDA and LDA, respectively) ices have been determined using reverse Monte Carlo, molecular dynamics, and lattice dynamics simulations. This combined approach leads to a more accurate and detailed structural description of HDA and LDA ices when compared to experiment than was previously possible. The water molecules in these ices form well connected hydrogen-bond networks that exhibit modes of vibration that extend throughout the solid and can involve up to 70% of all molecules. However, the networks display significant differences in their dynamical behavior. In HDA, the extended low-frequency vibrational modes occur in dense parallel two dimensional layers of water that are approximately 10 nm thick. In contrast, the extended modes in LDA resemble a holey structure that encapsulates many small pockets of nonparticipating water molecules. [ABSTRACT FROM AUTHOR]

We use density functional theory based nonequilibrium Green’s function to calculate the current through the different rodlike molecules at the finite temperatures self-consistently, which was compared to the experimental measurements presented by Reichert et al. [Phys. Rev. Lett. 88, 176804 (2002)] and by Mayor et al. [Angew. Chem. Int. Ed. 42, 5834 (2003)], respectively. Our results agree with the measurements very well, especially for the bias around ±1.0 V. The investigation of the topological effect for the symmetrical molecule reveals the fact that the para position compound provides a considerably larger conductance than the meta one. [ABSTRACT FROM AUTHOR]

Electronic transport properties of alkanedithiols are calculated by a first-principles method based on density functional theory and nonequilibrium Green’s function formalism. At small bias, the I-V characteristics are linear and the resistances conform to the Magoga’s exponential law. The calculated length-dependent decay constant γ which reflects the effect of internal molecular structure is in accordance with most experiments quantitatively. Also, the calculated effective contact resistance R0 is in good agreement with the results of repeatedly measuring molecule-electrode junctions [B. Xu and N. Tao, Science 301, 1221 (2003)]. [ABSTRACT FROM AUTHOR]

The bistable molecular switches have been studied theoretically based on the first-principles calculation. The geometry structures of the switches studied in this paper can be triggered between two symmetrical structures by using an external applied electric field. I-V characteristic curves of the different molecule configurations have been calculated, and distinguishability of these characteristic curves indicates a switching behavior, the performance of which can be improved significantly by some suitable donors and acceptors. [ABSTRACT FROM AUTHOR]

The quantum transport of a gated polythiophene nanodevice is analyzed using density functional theory and nonequilibrium Green’s function approach. For this typical molecular field effect transistor, we prove the existence of two main features of electronic components, i.e., negative differential resistance and good switching. Ab initio based explanations of these features are provided by distinguishing fixed and shifting conducting states, which are shown to arise from the interface and functional molecule, respectively. The results show that proper functional molecules can be used in conjunction with metallic electrodes to achieve basic electronics functionality at molecular length scales. [ABSTRACT FROM AUTHOR]

We use a self-consistent method to study the current of the single molecular transistor modulated by the transverse field in the level of the density functional theory and the nonequilibrium Green function method. The numerical results show that both the polyacene-dithiol molecules and the fused-ring thiophene molecules are the potential high-frequency molecular transistors controlled by the transverse field. The longer molecules of the polyacene-dithiol or the fused-ring thiophene are in favor of realizing the gate-bias controlled molecular transistor. The theoretical results suggest the related experiments. [ABSTRACT FROM AUTHOR]

We study theoretically the vertical electron transport in semiconductor multiple-quantum-well structures, where sequential tunneling between neighboring wells takes place. The nonuniformity of electric field along the growth axis and charge redistribution among the quantum wells, as well as between the inner wells and contacts, are taken into account. A simple and efficient model of charged contact layers is proposed. The calculated I-V curves exhibit regions of conventional N-shaped negative differential conductivity and Z-shaped portions of intrinsic bistability, both arising due to the tunneling resonances. A general explanation of their formation mechanism is given, which is valid for any form of interwell transitions of resonant nature. The conditions of N- and Z-shaped curve observation and controllable transition between them are discussed. [ABSTRACT FROM AUTHOR]

An ab initio study is used for analyzing the structural stability of carbon clathrates at high pressure and identifying fcc-[C.sub.135] clathrate as the third most stable carbon phase after cubic diamond and hexagonal graphite. Phonon dispersion calculations have confirmed the dynamic stability of fcc-[C.sub.136] along with diamond.

First-principles calculations were performed on the double-impurities-doped Ti[O.sub.2] in order to investigate the optimization of the conditions required for the synthesis of efficient spintronic devices. Results point out the possibility of development of systems where the highest occupied impurity states overlap well with the conduction band minimum by selecting suitable impurity pairs.

Investigates a body-centered-cubic lattice model with realistic many-body interactions to describe both crystalline and molten states of silicon. Energy of the atoms surrounded by tetrahedral first-neighbors; First-order transition between a solid with diamond structure and a melt; Nucleation and domain growth in certain range of supercooling.