66 research outputs found
Memory function formalism approach to electrical conductivity and optical response of dilute magnetic semiconductors
A combination of the memory function formalism and time-dependent
density-functional theory is applied to transport in dilute magnetic
semiconductors. The approach considers spin and charge disorder and
electron-electron interaction on an equal footing. Within the weak disorder
limit and using a simple parabolic approximation for the valence band we show
that Coulomb and exchange scattering contributions to the resistivity in GaMnAs
are of the same order of magnitude. The positional correlations of defects
result in a significant increase of Coulomb scattering, while the suppression
of localized spin fluctuations in the ferromagnetic phase contributes
substantially to the experimentally observed drop of resistivity below T_c. A
proper treatment of dynamical screening and collective excitations is essential
for an accurate description of infrared absorption.Comment: Proceedings of the 13th Brazilian Workshop on Semiconductors Physic
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
Response properties of III-V dilute magnetic semiconductors: interplay of disorder, dynamical electron-electron interactions and band-structure effects
A theory of the electronic response in spin and charge disordered media is
developed with the particular aim to describe III-V dilute magnetic
semiconductors like GaMnAs. The theory combines a detailed k.p description of
the valence band, in which the itinerant carriers are assumed to reside, with
first-principles calculations of disorder contributions using an
equation-of-motion approach for the current response function. A fully dynamic
treatment of electron-electron interaction is achieved by means of
time-dependent density functional theory. It is found that collective
excitations within the valence band significantly increase the carrier
relaxation rate by providing effective channels for momentum relaxation. This
modification of the relaxation rate, however, only has a minor impact on the
infrared optical conductivity in GaMnAs, which is mostly determined by the
details of the valence band structure and found to be in agreement with
experiment.Comment: 15 pages, 9 figure
Transport and optical conductivity in dilute magnetic semiconductors
doi: 10.1088/0953-8984/21/8/084202 http://iopscience.iop.org/0953-8984/21/8/084202/pdf/0953-8984_21_8_084202.pdfA theory of transport in spin and charge disordered media is developed, with a particular emphasis on dilute magnetic semiconductors. The approach is based on the equation of motion for the current-current response function and considers both spin and charge disorder and electron-electron interaction on an equal footing. The formalism is applied to the specific case
of Ga1−xMnxAs. Within the single parabolic band approximation it is shown that both spin
(p-d exchange) and charge (Coulomb) scattering contributions to the resistivity are of the same order of magnitude and should be treated simultaneously. Positional correlations of charged impurities are shown to significantly increase the Coulomb scattering. In the magnetically ordered phase, the suppression of localized spin fluctuations leads to a sizable reduction of spin scattering, which may contribute to the experimentally observed drop in resistivity below the critical temperature. The developed model allows for a comprehensive treatment of electron-electron interaction, screening and correlation effects by means of time-dependent density-functional theory. It is shown that collective modes and a dynamical treatment of electron-electron interaction are essential for an accurate description of the infrared absorption
spectrum.This work was supported by DOE grant no. DE-FG02-05ER46213
Enhanced carrier scattering rates in dilute magnetic semiconductors with correlated impurities
In III-V dilute magnetic semiconductors (DMSs) such as GaMnAs,
the impurity positions tend to be correlated, which can drastically affect the
electronic transport properties of these materials. Within the memory function
formalism we have derived a general expression for the current relaxation
kernel in spin and charge disordered media and have calculated spin and charge
scattering rates in the weak-disorder limit. Using a simple model for magnetic
impurity clustering, we find a significant enhancement of the charge
scattering. The enhancement is sensitive to cluster parameters and may be
controllable through post-growth annealing.Comment: 4 pages, 3 figure
Temperature-dependent resistivity of ferromagnetic GaMnAs: Interplay between impurity scattering and many-body effects
The static conductivity of the dilute magnetic semiconductor GaMnAs is
calculated using the memory function formalism and time-dependent
density-functional theory to account for impurity scattering and to treat
Hartree and exchange interactions within the hole gas. We find that the Coulomb
scattering off the charged impurities alone is not sufficient to explain the
experimentally observed drop in resistivity below the ferromagnetic transition
temperature: the often overlooked scattering off the fluctuations of localized
spins is shown to play a significant role
Mapping of quantum well eigenstates with semimagnetic probes
We present results of transmission measurements on CdTe quantum wells with
thin semimagnetic CdMnTe probe layers embedded in various positions along the
growth axis. The presence of the probes allow us to map the probability density
functions by two independent methods: analyzing the exciton energy position and
the exciton Zeeman splitting. We apply both approaches to map the first three
quantum well eigenstates and we find that both of them yield equally accurate
results.Comment: Accepted for publication in Physical Review
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