54,047 research outputs found
Positive mass theorems for asymptotically AdS spacetimes with arbitrary cosmological constant
We formulate and prove the Lorentzian version of the positive mass theorems
with arbitrary negative cosmological constant for asymptotically AdS
spacetimes. This work is the continuation of the second author's recent work on
the positive mass theorem on asymptotically hyperbolic 3-manifolds.Comment: 17 pages, final version, to appear in International Journal of
Mathematic
Spin injection from the Heusler alloy Co_2MnGe into Al_0.1Ga_0.9As/GaAs heterostructures
Electrical spin injection from the Heusler alloy Co_2MnGe into a p-i-n
Al_0.1Ga_0.9As/GaAs light emitting diode is demonstrated. A maximum
steady-state spin polarization of approximately 13% at 2 K is measured in two
types of heterostructures. The injected spin polarization at 2 K is calculated
to be 27% based on a calibration of the spin detector using Hanle effect
measurements. Although the dependence on electrical bias conditions is
qualitatively similar to Fe-based spin injection devices of the same design,
the spin polarization injected from Co_2MnGe decays more rapidly with
increasing temperature.Comment: 8 pages, 4 figure
Temperature dependent surface relaxations of Ag(111)
The temperature dependent surface relaxation of Ag(111) is calculated by
density-functional theory. At a given temperature, the equilibrium geometry is
determined by minimizing the Helmholtz free energy within the quasiharmonic
approximation. To this end, phonon dispersions all over the Brillouin zone are
determined from density-functional perturbation theory. We find that the
top-layer relaxation of Ag(111) changes from an inward contraction (-0.8 %) to
an outward expansion (+6.3%) as the temperature increases from T=0 K to 1150 K,
in agreement with experimental findings. Also the calculated surface phonon
dispersion curves at room temperature are in good agreement with helium
scattering measurements. The mechanism driving this surface expansion is
analyzed.Comment: 6 pages, 7 figures, submitted to Phys. Rev. B (May 1998). Other
related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
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