166 research outputs found
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
Manifestation of the spin-Hall effect through transport measurements in the mesoscopic regime
We study theoretically the manifestation of the spin-Hall effect in a
two-dimensional electronic system with Rashba spin-orbit coupling via
dc-transport measurements in realistic mesoscopic H-shape structures. The
Landauer-Buttiker formalism is used to model samples with mobilities and Rashba
coupling strengths of current experiments and to demonstrate the appearance of
a measurable Rashba-coupling dependent voltage. This type of measurement
requires only metal contacts, i.e., no magnetic elements are present. We also
confirm the robustness of the intrinsic spin-Hall effect against disorder in
the mesoscopic metallic regime in agreement with results of exact
diagonalization studies in the bulk.Comment: 5 pages, 3 figure
Charge Hall effect driven by spin-dependent chemical potential gradients and Onsager relations in mesoscopic systems
We study theoretically the spin-Hall effect as well as its reciprocal
phenomenon (a transverse charge current driven by a spin-dependent chemical
potential gradient) in electron and hole finite size mesoscopic systems. The
Landauer-Buttiker-Keldysh formalism is used to model samples with mobilities
and Rashba coupling strengths which are experimentally accessible and to
demonstrate the appearance of measurable charge currents induced by the
spin-dependent chemical potential gradient in the reciprocal spin-Hall effect.
We also demonstrate that within the mesoscopic coherent transport regime the
Onsager relations are fulfilled for the disorder averaged conductances for
electron and hole mesoscopic systems.Comment: 5 pages, 6 figures, typos correcte
The quantum Hall plateau transition at order 1/N
The localization behavior of noninteracting two-dimensional electrons in a
random potential and strong magnetic field is of fundamental interest for the
physics of the quantum Hall effect. In order to understand the emergence of
power-law delocalization near the discrete extended-state energies , we study a generalization of the disorder-averaged
Liouvillian framework for the lowest Landau level to flavors of electron
densities (N=1 for the physical case). We find analytically the large-N limit
and 1/N corrections for all disorder strengths: at this gives an
estimate of the critical conductivity, and at order 1/N an estimate of the
localization exponent . The localization properties of the analytically
tractable theory seem to be continuously connected to those of the
exact quantum Hall plateau transition at .Comment: 4 pages, 4 figures; improved text, 1 corrected referenc
Non-Drude Optical Conductivity of (III,Mn)V Ferromagnetic Semiconductors
We present a numerical model study of the zero-temperature infrared optical
properties of (III,Mn)V diluted magnetic semiconductors. Our calculations
demonstrate the importance of treating disorder and interaction effects
simultaneously in modelling these materials. We find that the conductivity has
no clear Drude peak, that it has a broadened inter-band peak near 220 meV, and
that oscillator weight is shifted to higher frequencies by stronger disorder.
These results are in good qualitative agreement with recent thin film
absorption measurements. We use our numerical findings to discuss the use of
f-sum rules evaluated by integrating optical absorption data for accurate
carrier-density estimates.Comment: 7 pages, 3 figure
Edge spin accumulation in semiconductor two-dimensional hole gases
The controlled generation of localized spin densities is a key enabler of
semiconductor spintronics In this work, we study spin Hall effect induced edge
spin accumulation in a two-dimensional hole gas with strong spin orbit
interactions. We argue that it is an intrinsic property, in the sense that it
is independent of the strength of disorder scattering. We show numerically that
the spin polarization near the edge induced by this mechanism can be large, and
that it becomes larger and more strongly localized as the spin-orbit coupling
strength increases, and is independent of the width of the conducting strip
once this exceeds the elastic scattering mean-free-path. Our experiments in
two-dimensional hole gas microdevices confirm this remarkable spin Hall effect
phenomenology. Achieving comparable levels of spin polarization by external
magnetic fields would require laboratory equipment whose physical dimensions
and operating electrical currents are million times larger than those of our
spin Hall effect devices.Comment: 6 pages, 5 figure
Infrared magneto-optical properties of (III,Mn)V ferromagetic semiconductors
We present a theoretical study of the infrared magneto-optical properties of
ferromagnetic (III,Mn)V semiconductors. Our analysis combines the kinetic
exchange model for (III,Mn)V ferromagnetism with Kubo linear response theory
and Born approximation estimates for the effect of disorder on the valence band
quasiparticles. We predict a prominent feature in the ac-Hall conductivity at a
frequency that varies over the range from 200 to 400 meV, depending on Mn and
carrier densities, and is associated with transitions between heavy-hole and
light-hole bands. In its zero frequency limit, our Hall conductivity reduces to
the -space Berry's phase value predicted by a recent theory of the
anomalous Hall effect that is able to account quantitatively for experiment. We
compute theoretical estimates for magnetic circular dichroism, Faraday
rotation, and Kerr effect parameters as a function of Mn concentration and free
carrier density. The mid-infrared response feature is present in each of these
magneto-optical effects.Comment: 11 pages, 5 figure
First Principles Calculation of Anomalous Hall Conductivity in Ferromagnetic bcc Fe
We perform a first principles calculation of the anomalous Hall effect in
ferromagnetic bcc Fe. Our theory identifies an intrinsic contribution to the
anomalous Hall conductivity and relates it to the k-space Berry phase of
occupied Bloch states. The theory is able to account for both dc and
magneto-optical Hall conductivities with no adjustable parameters.Comment: 4 pages, 6 figures, author list correcte
Charge and Spin Currents Generated by Dynamical Spins
We demonstrate theoretically that a charge current and a spin current are
generated by spin dynamics in the presence of spin-orbit interaction in the
perturbative regime. We consider a general spin-orbit interaction including the
spatially inhomogeneous case. Spin current due to spin damping is identified as
one origin of generated charge current, but other contributions exist, such as
the one due to an induced conservative field and the one arising from the
inhomogeneity of spin-orbit interaction.Comment: 14 pages, 4 figure
Anomalous Hall effect in a two-dimensional electron gas
The anomalous Hall effect in a magnetic two-dimensional electron gas with
Rashba spin-orbit coupling is studied within the Kubo-Streda formalism in the
presence of pointlike potential impurities. We find that all contributions to
the anomalous Hall conductivity vanish to leading order in disorder strength
when both chiral subbands are occupied. In the situation that only the majority
subband is occupied, all terms are finite in the weak scattering limit and the
total anomalous Hall conductivity is dominated by skew scattering. We compare
our results to previous treatments and resolve some of the discrepancies
present in the literature.Comment: 11 pages, 5 figure
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