58,252 research outputs found
NMR Probing Spin Excitations in the Ring-Like Structure of a Two-Subband System
Resistively detected nuclear magnetic resonance (NMR) is observed inside the
ring-like structure, with a quantized Hall conductance of 6e^2/h, in the phase
diagram of a two subband electron system. The NMR signal persists up to 400 mK
and is absent in other states with the same quantized Hall conductance. The
nuclear spin-lattice relaxation time, T1, is found to decrease rapidly towards
the ring center. These observations are consistent with the assertion of the
ring-like region being a ferromagnetic state that is accompanied by collective
spin excitations.Comment: 4 pages, 4 figure
Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions
By use of first-principles electronic structure calculations, we predict that
the magnetoresistance of the bcc Co(100)/MgO(100)/bcc Co(100) and
FeCo(100)/MgO(100)/FeCo(100) tunneling junctions can be several times larger
than the very large magnetoresistance predicted for the
Fe(100)/MgO(100)/Fe(100) system. The origin of this large magnetoresistance can
be understood using simple physical arguments by considering the electrons at
the Fermi energy travelling perpendicular to the interfaces. For the minority
spins there is no state with symmetry whereas for the majority spins
there is only a state. The state decays much more slowly
than the other states within the MgO barrier. In the absence of scattering
which breaks the conservation of momentum parallel to the interfaces, the
electrons travelling perpendicular to the interfaces undergo total reflection
if the moments of the electrodes are anti-parallel. These arguments apply
equally well to systems with other well ordered tunnel barriers and for which
the most slowly decaying complex energy band in the barrier has
symmetry. Examples include systems with (100) layers constructed from Fe, bcc
Co, or bcc FeCo electrodes and Ge, GaAs, or ZnSe barriers.Comment: 8 figure files in eps forma
First-principles study of phenyl ethylene oligomers as current-switch
We use a self-consistent method to study the distinct current-switch of
-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol, from
the first-principles calculations. The numerical results are in accord with the
early experiment [Reed et al., Sci. Am. \textbf{282}, 86 (2000)]. To further
investigate the transport mechanism, we calculate the switching behavior of
p-terphenyl with the rotations of the middle ring as well. We also study the
effect of hydrogen atom substituting one ending sulfur atom on the transport
and find that the asymmetry of I-V curves appears and the switch effect still
lies in both the positive and negative bias range.Comment: 6 pages, 6 figure
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