Spin-polarized currents generated by magnetic Fe atomic chains

Fe-based devices are widely used in spintronics because of high spin-polarization and magnetism. In this work, free-standing Fe atomic chains were proposed to be used as the thinnest wires to generate spin-polarized currents due to the spin-polarized energy bands. By ab initio calculations, the zigzag structure was found more stable than the wide-angle zigzag structure and has higher ratio of spin-up and spin-down currents. By our theoretical prediction, Fe atomic chains have sufficiently long thermal lifetime only at T<=150 K, while C atomic chains are very stable even at T=1000 K. This result means that the spintronic devices based on Fe chains could only work at low temperature. A system constructed by a short Fe chain sandwiched between two graphene electrodes was proposed as a spin-polarized current generator, while a C chain does not have such property. The present work may be instructive and meaningful to further practical applications based on recent technical development on the preparation of metal atomic chains [Proc. Natl. Acad. Sci. U.S.A. 107, 9055 (2010)].Comment: Nanotechnology (2014

Retrieving the Size of Deep-subwavelength Objects via Tunable Optical Spin-Orbit Coupling

We propose a scheme to retrieve the size parameters of a nano-particle on a glass substrate at a scale much smaller than the wavelength. This is achieved by illuminating the particle using two plane waves to create rich and non-trivial local polarization distributions, and observing the far-field scattering pattern into the substrate. A simple dipole model which exploits tunneling effect of evanescent field into regions beyond the critical angle, as well as directional scattering due to spin-orbit coupling is developed, to relate the particle's shape, size and position to the far-field scattering with remarkable sensitivity. Our method brings about a far-field super-resolution imaging scheme based on the interaction of vectorial light with nanoparticles

Non-negligible magnetic dipole scattering from metallic nanowire for ultrasensitive deflection sensing

It is generally believed that when a single metallic nanowire is sufficiently small, it scatters like a point electric dipole. We show theoretically when a metallic nanowire is placed inside specially designed beams, the non-negligible magnetic dipole contribution along with the electric dipole resonance can lead to unidirectional scattering in the far-field, fulfilling Kerker's condition. Remarkably, this far-field unidirectional scattering encodes information that is highly dependent on the nanowire's deflection at a scale much smaller than the wavelength. The special role of small but non-negligible magnetic response and plasmonic resonance are highlighted for this extreme sensitivity as compared with the dielectric counterpart. Effects such as scattering efficiency and shape of the nanowire's cross section are also discussed.Comment: 5 pages, 3 figures. Comments are welcom

Hidden force opposing ice compression

Coulomb repulsion between the unevenly-bound bonding and nonbonding electron pairs in the O:H-O hydrogen-bond is shown to originate the anomalies of ice under compression. Consistency between experimental observations, density functional theory and molecular dynamics calculations confirmed that the resultant force of the compression, the repulsion, and the recovery of electron-pair dislocations differentiates ice from other materials in response to pressure. The compression shortens and strengthens the longer-and-softer intermolecular O:H lone-pair virtual-bond; the repulsion pushes the bonding electron pair away from the H+/p and hence lengthens and weakens the intramolecular H-O real-bond. The virtual-bond compression and the real-bond elongation symmetrize the O:H-O as observed at ~60 GPa and result in the abnormally low compressibility of ice. The virtual-bond stretching phonons (< 400 cm-1) are thus stiffened and the real-bond stretching phonons (> 3000 cm-1) softened upon compression. The cohesive energy of the real-bond dominates and its loss lowers the critical temperature for the VIII-VII phase transition. The polarization of the lone electron pairs and the entrapment of the bonding electron pairs by compression expand the band gap consequently. Findings should form striking impact to understanding the physical anomalies of H2O.Comment: arXiv admin note: text overlap with arXiv:1110.007