Verlag des Forschungszentrums Jülich
JUEL-4090
In this thesis a new method is established, based on the combination of the embedding
Green-function method and the full-potentiallinearized augmented plane-wave
(FLAPW) method, to describe the coherent and the sequential electron transport
through realistic systems. By use of the density functional theory (DFT) material
depended properties of realistic systems can be described on the atomic scale. The
FLAPW method is today one of the most reliable and precise numerical methods
available for first-principle electronic structure calculations based on the DFT. However,
different to standard problems of a periodic solid, the description of electron
transport requires the treatment of the scattering problem. This is particularly difficult
when described with a plane-wave basis. Thus, a key part of the present thesis
is devoted to the development of a new computational scheme which is able to deal
with a scattering region sandwiched between two semi- infinite leads. Realizing the
ideas put forward by J. Inglesfield, the existing FLEUR code is modified to calculate
the single-electron Green function for the embedded scattering region. The semi-
infinite leads are described in terms of a transfer-matrix formalism which enables
one to obtain the so-calIed complex bandstructure of bulk materials.
The electron transport is described using either the Landauer model or Bardeen 's
formalism of tunneling. These two formulas are discussed as two different limits
of single-particle transport and their reformulation in terms of quantities readily
available from the embedding method is presented.
Besides the presentation of the theory and the details of its implementation the thesis
describes how the method has been applied to several different test systems to validate
the implementation. The spin-dependent transport properties of a Fe/MgO/Fe
tunneljunction, the model system of tunnel-magnetoresistance (TMR), were investigated.
It is shown that the details of the Fe/MgO interface in this junction is
of crucial importance for the tunneling conductance. While the pure relaxation of
a Fe/MgO interface already changes the conductance, even more drastic modifications
are found as soon as one FeO layer is inserted or if the interface is modified by
interchanging the Mg and O atoms.
Wortmann, Daniel
An Embedding Green Function Approach for Electron Transport through Interfaces
IV, 142 S., 2003
The theoretical description of electron transport properties through nanoscale systems
is one of the major challenges of contemporary solid state physics. Magneto-
electronics, spin-electronics or molecular-electronics are emerging new fields with a
great potential for future nano-electronics.
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