12 research outputs found
GW method applied to localized 4f electron systems
We apply a recently developed quasiparticle self-consistent method
(QSGW) to Gd, Er, EuN, GdN, ErAs, YbN and GdAs. We show that QSGW combines
advantages separately found in conventional and LDA+ theory, in a
simple and fully \emph{ab initio} way. \qsgw reproduces the experimental
occupied levels well, though unoccupied levels are systematically
overestimated. Properties of the Fermi surface responsible for electronic
properties are in good agreement with available experimental data. GdN is
predicted to be very near a critical point of a first-order metal-insulator
transition.Comment: 5 pages,3 figures, 2 table
Ab-initio calculations of spin tunneling through an indirect barrier
We use a fully relativistic layer Green's functions approach to investigate
spin-dependent tunneling through a symmetric indirect band gap barrier like
GaAs/AlAs/GaAs heterostructure along [100] direction. The method is based on
Linear Muffin Tin Orbitals and it is within the Density Functional Theory (DFT)
in the Local Density Approximation (LDA). We find that the results of our {\it
ab-initio} calculations are in good agreement with the predictions of our
previous empirical tight binding model [Phys. Rev. {\bf B}, 075313 (2006)]. In
addition we show the -dependence of the spin polarization which we did
not previously include in the model. The {\it ab-initio} calculations indicate
a strong -dependence of the transmission and the spin polarization due
to band non-parabolicity. A large window of 25-50 % spin polarization was found
for a barrier of 8 AlAs monolayers at = 0.03 . Our
calculations show clearly that the appearance of energy windows with
significant spin polarization depends mostly on the location of transmission
resonances and their corresponding zeros and not on the magnitude of the spin
splitting in the barrier.Comment: 10 pages, 3 figure
Detection of the spin character of Fe(001) surface states by scanning tunneling microscopy: A theoretical proposal
We consider the magnetic structure on the Fe(001) surface and theoretically
study the scanning tunneling spectroscopy using a spin-polarized tip (SP-STM).
We show that minority-spin surface states induce a strong bias dependence of
the tunneling differential conductance which largely depends on the orientation
of the magnetization in the SP-STM tip relative to the easy magnetization axis
in the Fe(001) surface. We propose to use this effect in order to determine the
spin character of the Fe(001) surface states. This technique can be applied
also to other magnetic surfaces in which surface states are observed.Comment: 5 pages, 4 figure
Many-body Electronic Structure of Metallic alpha-Uranium
We present results for the electronic structure of alpha uranium using a
recently developed quasiparticle self-consistent GW method (QSGW). This is the
first time that the f-orbital electron-electron interactions in an actinide has
been treated by a first-principles method beyond the level of the generalized
gradient approximation (GGA) to the local density approximation (LDA). We show
that the QSGW approximation predicts an f-level shift upwards of about 0.5 eV
with respect to the other metallic s-d states and that there is a significant
f-band narrowing when compared to LDA band-structure results. Nonetheless,
because of the overall low f-electron occupation number in uranium,
ground-state properties and the occupied band structure around the Fermi energy
is not significantly affected. The correlations predominate in the unoccupied
part of the f states. This provides the first formal justification for the
success of LDA and GGA calculations in describing the ground-state properties
of this material.Comment: 4 pages, 3 fihgure
Strain-Induced Conduction Band Spin Splitting in GaAs from First Principles Calculations
We use a recently developed self-consistent GW approximation to present first
principles calculations of the conduction band spin splitting in GaAs under
[110] strain. The spin orbit interaction is taken into account as a
perturbation to the scalar relativistic hamiltonian. These are the first
calculations of conduction band spin splitting under deformation based on a
quasiparticle approach; and because the self-consistent GW scheme accurately
reproduces the relevant band parameters, it is expected to be a reliable
predictor of spin splittings. We also discuss the spin relaxation time under
[110] strain and show that it exhibits an in-plane anisotropy, which can be
exploited to obtain the magnitude and sign of the conduction band spin
splitting experimentally.Comment: 8 pages, 4 figures, 1 tabl
Prediction of large linear-in-k spin splitting for holes in the 2D GaAs/AlAs system
The spin-orbit interaction generally leads to spin splitting (SS) of electron
and hole energy states in solids, a splitting that is characterized by a
scaling with the wavevector . Whereas for {\it 3D bulk zincblende}
solids the electron (heavy hole) SS exhibits a cubic (linear) scaling with ,
in {\it 2D quantum-wells} the electron (heavy hole) SS is currently believed to
have a mostly linear (cubic) scaling. Such expectations are based on using a
small 3D envelope function basis set to describe 2D physics. By treating
instead the 2D system explicitly in a multi-band many-body approach we discover
a large linear scaling of hole states in 2D. This scaling emerges from hole
bands coupling that would be unsuspected by the standard model that judges
coupling by energy proximity. This discovery of a linear Dresselhaus k-scaling
for holes in 2D implies a different understanding of hole-physics in
low-dimensions.Comment: 5 figures and 1 Tabl
Reversal of spin polarization in Fe/GaAs (001) driven by resonant surface states: First-principles calculations
A minority-spin resonant state at the Fe/GaAs(001) interface is predicted to
reverse the spin polarization with voltage bias of electrons transmitted across
this interface. Using a Green's function approach within the local spin density
approximation we calculate spin-dependent current in a Fe/GaAs/Cu tunnel
junction as a function of applied bias voltage. We find a change in sign of the
spin polarization of tunneling electrons with bias voltage due to the interface
minority-spin resonance. This result explains recent experimental data on spin
injection in Fe/GaAs contacts and on tunneling magnetoresistance in Fe/GaAs/Fe
magnetic tunnel junctions
Tunneling anisotropic magnetoresistance driven by resonant surface states: First-principles calculations of Fe(001) surface
Fully-relativistic first-principles calculations of the Fe(001) surface
demonstrate that resonant surface (interface) states may produce sizeable
tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a
single magnetic electrode. The effect is driven by the spin-orbit coupling. It
shifts the resonant surface band via the Rashba effect when the magnetization
direction changes. We find that spin-flip scattering at the interface is
controlled not only by the strength of the spin-orbit coupling, but depends
strongly on the intrinsic width of the resonant surface states.Comment: 5 pages, 3 figure
Questaal: A package of electronic structure methods based on the linear muffin-tin orbital technique
This paper summarises the theory and functionality behind Questaal, an open-source suite of codes for calculating the electronic structure and related properties of materials from first principles. The formalism of the linearised muffin-tin orbital (LMTO) method is revisited in detail and developed further by the introduction of short-ranged tight-binding basis functions for full-potential calculations. The LMTO method is presented in both Green's function and wave function formulations for bulk and layered systems. The suite's full-potential LMTO code uses a sophisticated basis and augmentation method that allows an efficient and precise solution to the band problem at different levels of theory, most importantly density functional theory, LDA+U, quasi-particle self-consistent GW and combinations of these with dynamical mean field theory. This paper details the technical and theoretical bases of these methods, their implementation in Questaal, and provides an overview of the code's design and capabilities. Program summary: Program Title: Questaal Program Files doi: http://dx.doi.org/10.17632/35jxxtzpdn.1 Code Ocean Capsule: https://doi.org/10.24433/CO.3778701.v1 Licensing provisions: GNU General Public License, version 3 Programming language: Fortran, C, Python, Shell Nature of problem: Highly accurate ab initio calculation of the electronic structure of periodic solids and of the resulting physical, spectroscopic and magnetic properties for diverse material classes with different strengths and kinds of electronic correlation. Solution method: The many electron problem is considered at different levels of theory: density functional theory, many body perturbation theory in the GW approximation with different degrees of self consistency (notably quasiparticle self-consistent GW) and dynamical mean field theory. The solution to the single-particle band problem is achieved in the framework of an extension to the linear muffin-tin orbital (LMTO) technique including a highly precise and efficient full-potential implementation. An advanced fully-relativistic, non-collinear implementation based on the atomic sphere approximation is used for calculating transport and magnetic properties.</p