4,198 research outputs found
Dissipation through spin Coulomb drag in electronic spin dynamics
Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for
spin currents in metals and semiconductors. We discuss the power loss due to
SCD in potential spintronics devices and analyze in detail the associated
damping of collective spin-density excitations. It is found that SCD
contributes substantially to the linewidth of intersubband spin plasmons in
parabolic quantum wells, which suggests the possibility of a purely optical
quantitative measurement of the SCD effect by means of inelastic light
scattering
Dissipation through spin Coulomb drag in electronic spin transport and optical excitations
Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for spin currents in metals and semiconductors. We discuss the power loss due to SCD in potential spintronics devices and analyze in detail the associated damping of collective spin-density excitations. It is found that SCD contributes substantially to the linewidth of intersubband spin plasmons in semiconductor quantum wells, which suggests the possibility of a purely optical quantitative measurement of the SCD effect in a parabolic well through inelastic light scattering
Intersubband spin-orbit coupling and spin splitting in symmetric quantum wells
In semiconductors with inversion asymmetry, spin-orbit coupling gives rise to
the well-known Dresselhaus and Rashba effects. If one considers quantum wells
with two or more conduction subbands, an additional, intersubband-induced
spin-orbit term appears whose strength is comparable to the Rashba coupling,
and which remains finite for symmetric structures. We show that the conduction
band spin splitting due to this intersubband spin-orbit coupling term is
negligible for typical III-V quantum wells
Nonuniqueness in spin-density-functional theory on lattices
In electronic many-particle systems, the mapping between densities and spin
magnetizations, {n(r), m(r)}, and potentials and magnetic fields, {v(r), B(r)},
is known to be nonunique, which has fundamental and practical implications for
spin-density-functional theory (SDFT). This paper studies the nonuniqueness
(NU) in SDFT on arbitrary lattices. Two new, non-trivial cases are discovered,
here called local saturation and global noncollinear NU, and their properties
are discussed and illustrated. In the continuum limit, only some well-known
special cases of NU survive.Comment: 4 pages, 1 figur
Non-adiabatic electron dynamics in time-dependent density-functional theory
Time-dependent density-functional theory (TDDFT) treats dynamical exchange
and correlation (xc) via a single-particle potential, Vxc(r,t), defined as a
nonlocal functional of the density n(r',t'). The popular adiabatic
local-density approximation (ALDA) for Vxc(r,t) uses only densities at the same
space-time point (r,t). To go beyond the ALDA, two local approximations have
been proposed based on quantum hydrodynamics and elasticity theory: (a) using
the current as basic variable (C-TDDFT) [G. Vignale, C. A. Ullrich, and S.
Conti, Phys. Rev. Lett. 79, 4878 (1997)], (b) working in a co-moving Lagrangian
reference frame (L-TDDFT) [I. V. Tokatly, Phys. Rev. B 71, 165105 (2005)]. This
paper illustrates, compares, and analyzes both non-adiabatic theories for
simple time-dependent model densities in the linear and nonlinear regime, for a
broad range of time and frequency scales. C- and L-TDDFT are identical in
certain limits, but in general exhibit qualitative and quantitative differences
in their respective treatment of elastic and dissipative electron dynamics. In
situations where the electronic density rapidly undergoes large deformations,
it is found that non-adiabatic effects can become significant, causing the ALDA
to break down.Comment: 15 pages, 15 figure
Differential cross sections for K-shell ionization by electron or positron impact
We have investigated the universal scaling behavior of differential cross
sections for the single K-shell ionization by electron or positron impact. The
study is performed within the framework of non-relativistic perturbation
theory, taking into account the one-photon exchange diagrams. In the case of
low-energy positron scattering, the doubly differential cross section exhibits
prominent interference oscillations. The results obtained are valid for
arbitrary atomic targets with moderate values of nuclear charge number Z.Comment: 13 pages, 7 figure
Time-dependent density functional theory on a lattice
A time-dependent density functional theory (TDDFT) for a quantum many-body
system on a lattice is formulated rigorously. We prove the uniqueness of the
density-to-potential mapping and demonstrate that a given density is
-representable if the initial many-body state and the density satisfy
certain well defined conditions. In particular, we show that for a system
evolving from its ground state any density with a continuous second time
derivative is -representable and therefore the lattice TDDFT is guaranteed
to exist. The TDDFT existence and uniqueness theorem is valid for any connected
lattice, independently of its size, geometry and/or spatial dimensionality. The
general statements of the existence theorem are illustrated on a pedagogical
exactly solvable example which displays all details and subtleties of the proof
in a transparent form. In conclusion we briefly discuss remaining open problems
and directions for a future research.Comment: 12 pages, 1 figur
Magnetic-dipole transition probabilities in B-like and Be-like ions
The magnetic-dipole transition probabilities between the fine-structure
levels (1s^2 2s^2 2p) ^2P_1/2 - ^2P_3/2 for B-like ions and (1s^2 2s 2p) ^3P_1
- ^3P_2 for Be-like ions are calculated. The configuration-interaction method
in the Dirac-Fock-Sturm basis is employed for the evaluation of the
interelectronic-interaction correction with negative-continuum spectrum being
taken into account. The 1/Z interelectronic-interaction contribution is derived
within a rigorous QED approach employing the two-time Green function method.
The one-electron QED correction is evaluated within framework of the anomalous
magnetic-moment approximation. A comparison with the theoretical results of
other authors and with available experimental data is presented
Estimation of carrier life time from intrinsic photoluminescence of ZnO
Comprehensive knowledge of the optical properties, particularly of the room
temperature (RT) photoluminescence (PL), of ZnO is essential for the future employment of this wideband
gap (~3.3 eV at 300 K) II-VI compound semiconductor in photonic and optoelectronic device
structures [1]. Hence, vigorous research activities on ZnO thin films, epilayers, and crystals took place
during the last two decades, encompassing a vast variety of effects and phenomena such as birefringence,
photocurrent, PL including sub-band gap emission, reflectance, transmittance, excitonic properties,
Raman modes, and absorption edge steepness [1-4]. However, despite that large body of knowledge and
its essential importance for light emitting processes, a discussion of the ZnO PL lineshape is not found
in the literature [5]
Intrinsic photoluminescence stokes shift in thin-film cadmium sulfide
Exciting a semiconductor through light absorption produces photoluminescence (PL).
In general, the emitted energy is lower than the energy absorbed. The phenomenon, first discovered
in the nineteenth century, is known as Stokes shift energy [1]. The change in energy (AS t o k e s), crucial
for the information about the phonon relaxation in the material and with importance in light emitting
devices, has not been investigated experimentally very systematically [2]. In this project, we present the
observation of the intrinsic photoluminescence Stokes shift in a semiconductor
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