8,100 research outputs found
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
- …