406 research outputs found
Co-planar spin-polarized light emitting diode
Studies of spin manipulation in semiconductors has benefited from the
possibility to grow these materials in high quality on top of optically active
III-V systems. The induced electroluminescence in these layered semiconductor
heterostructures has been used for a reliable spin detection. In semiconductors
with strong spin-orbit interaction, the sensitivity of vertical devices may be
insufficient, however, because of the sepration of the spin aligner part and
the spin detection region by one or more heterointerfaces and becuse of the
short spin coherence length. Here we demostrate that higly sensitive spin
detection can be achieved using a lateral arrangement of the spin polarized and
optically active regions. Using our co-planar spin-polarized light emitting
diodes we detect electrical field induced spin generation in a semiconductor
heterojunction two-dimensional hole gas. The polarization results from spin
asymmetric recombination of injected electrons with strongly SO coupled
two-dimensional holes. The possibility to detect magnetized Co particles
deposited on the co-planar diode structure is also demonstrated.Comment: 8 pages, 3 figure
Gilbert damping and spin Coulomb drag in a magnetized electron liquid with spin-orbit interaction
We present a microscopic calculation of the Gilbert damping constant for the
magnetization of a two-dimensional spin-polarized electron liquid in the
presence of intrinsic spin-orbit interaction. First we show that the Gilbert
constant can be expressed in terms of the auto-correlation function of the
spin-orbit induced torque. Then we specialize to the case of the Rashba
spin-orbit interaction and we show that the Gilbert constant in this model is
related to the spin-channel conductivity. This allows us to study the Gilbert
damping constant in different physical regimes, characterized by different
orderings of the relevant energy scales -- spin-orbit coupling, Zeeman
coupling, momentum relaxation rate, spin-momentum relaxation rate, spin
precession frequency -- and to discuss its behavior in various limits.
Particular attention is paid to electron-electron interaction effects,which
enter the spin conductivity and hence the Gilbert damping constant via the spin
Coulomb drag coefficient.Comment: 18 pages, 8 figure
Large Tunneling Anisotropic Magneto-Seebeck Effect in a CoPt|MgO|Pt Tunnel Junction
We theoretically investigate the Tunneling Anisotropic Magneto-Seebeck effect
in a realistically-modeled CoPt|MgO|Pt tunnel junction using coherent transport
calculations. For comparison we study the tunneling magneto-Seebeck effect in
CoPt|MgO|CoPt as well. We find that the magneto-Seebeck ratio of CoPt|MgO|Pt
exceeds that of CoPt|MgO|CoPt for small barrier thicknesses, reaching 175% at
room temperature. This result provides a sharp contrast to the
magnetoresistance, which behaves oppositely for all barrier thicknesses and
differs by one order of magnitude between devices. Here the magnetoresistance
results from differences in transmission brought upon by changing the tunnel
junction's magnetization configuration. The magneto-Seebeck effect results from
variations in asymmetry of the energy-dependent transmission instead. We report
that this difference in origin allows for CoPt|MgO|Pt to possess strong thermal
magnetic-transport anisotropy.Comment: 6 pages, 6 figure
Electronic structure of ferromagnetic semiconductor Ga1-xMnxAs probed by sub-gap magneto-optical spectroscopy
We employ Faraday and Kerr effect spectroscopy in the infrared range to
investigate the electronic structure of Ga1-xMnxAs near the Fermi energy. The
band structure of this archetypical dilute-moment ferromagnetic semiconductor
has been a matter of controversy, fueled partly by previous measurements of the
unpolarized infrared absorption and their phenomenological impurity-band
interpretation. The infrared magneto-optical effects we study arise directly
from the spin-splitting of the carrier bands and their chiral asymmetry due to
spin-orbit coupling. Unlike the unpolarized absorption, they are intimately
related to ferromagnetism and their interpretation is much more microscopically
constrained in terms of the orbital character of the relevant band states. We
show that the conventional theory of the disordered valence band with dominant
As p-orbital character and coupled by kinetic-exchange to Mn local moments
accounts semi-quantitatively for the overall characteristics of the measured
infrared magneto-optical spectra.Comment: 4 pages 3 figure
Experimental observation of the spin-Hall effect in a two dimensional spin-orbit coupled semiconductor system
We report the experimental observation of the spin-Hall effect in a
two-dimensional (2D) hole system with Rashba spin-orbit coupling.
The 2D hole layer is a part of a p-n junction light-emitting diode with a
specially designed co-planar geometry which allows an angle-resolved
polarization detection at opposite edges of the 2D hole system. In equilibrium
the angular momenta of the Rashba split heavy hole states lie in the plane of
the 2D layer. When an electric field is applied across the hole channel a non
zero out-of-plane component of the angular momentum is detected whose sign
depends on the sign of the electric field and is opposite for the two edges.
Microscopic quantum transport calculations show only a weak effect of disorder
suggesting that the clean limit spin-Hall conductance description (intrinsic
spin-Hall effect) might apply to our system.Comment: 4 pages, 3 figures, paper based on work presented at the Gordon
Research Conference on Magnetic Nano-structures (August 2004) and Oxford Kobe
Seminar on Spintronics (September 2004); accepted for publication in Physical
Review Letters December 200
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