18,491 research outputs found
Unusual magnetoresistance in a topological insulator with a single ferromagnetic barrier
Tunneling surface current through a thin ferromagnetic barrier in a
three-dimensional topological insulator is shown to possess an extraordinary
response to the orientation of barrier magnetization. In contrast to
conventional magnetoresistance devices that are sensitive to the relative
alignment of two magnetic layers, a drastic change in the transmission current
is achieved by a single layer when its magnetization rotates by 90 degrees.
Numerical estimations predict a giant magnetoresistance as large as 800 % at
room temperature and the proximate exchange interaction of 40 meV in the
barrier. When coupled with electrical control of magnetization direction, this
phenomenon may be used to enhance the gating function with potentially sharp
turn-on/off for low power applications
One-loop Neutron Electric Dipole Moment from Supersymmetry without R-parity
We present a detailed analysis together with exact numerical calculations on
one-loop contributions to neutron electric dipole moment from supersymmetry
without R-parity, focusing on the gluino, chargino, and neutralino
contributions. Apart from the neglected family mixing among quarks, complete
formulae are given for the various contributions, through the quark dipole
operators, to which the present study is restricted. We discuss the structure
and main features of the R-parity violating contributions and the interplay
between the R-parity conserving and violating parameters. In particular, the
parameter combination , under the optimal
parametrization adopted, is shown to be solely responsible for the R-parity
violating contributions in the supersymmetric loop diagrams. While
could bear a complex phase, the latter is not
necessary to have a R-parity violating contribution.Comment: 43 pages Revtex with 15 eps- and 4 ps- figure files incoporated;
proofread version to be published in Phys. Rev.
A Detailed Analysis of One-loop Neutrino Masses from the Generic Supersymmetric Standard Model
In the generic supersymmetric standard model which had no global symmetry
enforced by hand, lepton number violation is a natural consequence.
Supersymmetry, hence, can be considered the source of experimentally demanded
beyond standard model properties for the neutrinos. With an efficient
formulation of the model, we perform a comprehensive detailed analysis of all
one-loop contributions to neutrino masses.Comment: 27 pages Revtex, no figur
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Research on VCSEL interference analysis and elimination method
Laser methane gas sensors have been increasingly accepted in coal mine safety monitoring. Most laser spectroscopic methane gas sensors are based in BFB lasers at around 1650nm. However, they suffer from high power consumption and high cost due to temperature control is required for laser diode operation at constant temperature. VCSEL lasers have offered low operation current and low power consumption when operating at non-TEC mode. However, it is found that the interference noise is critical for laser methane detection. This paper report typical results of the laser diode ripple characterization method and methods of noise reduction methods are discussed
Binding energies and electronic structures of adsorbed titanium chains on carbon nanotubes
We have studied the binding energies and electronic structures of metal (Ti,
Al, Au) chains adsorbed on single-wall carbon nanotubes (SWNT) using first
principles methods. Our calculations have shown that titanium is much more
favored energetically over gold and aluminum to form a continuous chain on a
variety of SWNTs. The interaction between titanium and carbon nanotube
significantly modifies the electronic structures around Fermi energy for both
zigzag and armchair tubes. The delocalized 3d electrons from the titanium chain
generate additional states in the band gap regions of the semiconducting tubes,
transforming them into metals.Comment: 4 pages, 3 figure
Electronic structure and magnetism of equiatomic FeN
In order to investigate the phase stability of equiatomic FeN compounds and
the structure-dependent magnetic properties, the electronic structure and total
energy of FeN with NaCl, ZnS and CsCl structures and various magnetic
configurations are calculated using the first-principles TB-LMTO-ASA method.
Among all the FeN phases considered, the antiferromagnetic NaCl structure with
q=(00pi) is found to have the lowest energy at the theoretical equilibrium
volume. However, the FM NaCl phase lies only 1mRyd higher. The estimated
equilibrium lattice constant for nonmagnetic ZnS-type FeN agrees quite well
with the experimental value, but for the AFM NaCl phase the estimated value is
6.7% smaller than that observed experimentally. For ZnS-type FeN, metastable
magnetic states are found for volumes larger than the equilibrium value. On the
basis of an analysis of the atom- and orbital-projected density of states and
orbital-projected Crystal Orbital Hamilton Population, the iron-nitrogen
interactions in NM ZnS, AFM NaCl and FM CsCl structures are discussed. The
leading Fe-N interactions is due to the d-p iron-nitrogen hybridization, while
considerable s-p and p-p hybridizations are also observed in all three phases.
The iron magnetic moment in FeN is found to be highly sensitive to the
nearest-neighboring Fe-N distance. In particular, the magnetic moment shows an
abrupt drop from a value of about 2 muB to zero with the reduction of the Fe-N
distance for the ZnS and CsCl structures.Comment: 12 pages, 6 figure
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