698,491 research outputs found
Unipolar and bipolar fatigue in antiferroelectric lead zirconate thin films and evidences for switching-induced charge injection inducing fatigue
For the first time, we show that unipolar fatigue does occur in
antiferroelectric capacitors, confirming the predictions of a previous work
[Appl. Phys. Lett., 94, 072901 (2009)]. We also show that unipolar fatigue in
antiferroelectrics is less severe than bipolar fatigue if the driving field is
of the same magnitude. This phenomenon has been attributed to the
switching-induced charge injection, the main cause for polarization fatigue in
ferroelectric and antiferroelectric materials. Other evidences for polarization
fatigue caused by the switching-induced charge injection from the nearby
electrode rather than the charge injection during stable/quasi-stable leakage
current stage are also discussed.Comment: 10 pages and 2 figure
First-principles investigation of transient current of molecular devices by using complex absorbing potential
Based on the non-equilibrium Green's function (NEGF) coupled with density
function theory (DFT), namely, NEGF-DFT quantum transport theory, we propose an
efficient formalism to calculate the transient current of molecular devices
under a step-like pulse from first principles. By combining NEGF-DFT with the
complex absorbing potential (CAP), the computational complexity of our
formalism (NEGF-DFT-CAP) is proportional to \emph{O}(N) where is the
number of time steps in the time-dependent transient calculation. Compared with
state-of-the-art algorithm of first principles time-dependent calculation that
scales with at least , this order N technique drastically reduces the
computational burden making it possible to tackle realistic molecular devices.
To ensure the accuracy of our method, we carry out the benchmark calculation
compared with exact NEGF-TDDFT formalism and they agree well with each other.
As an illustration, we investigate the transient current of molecular device
Al-C-Al from first principles
Finite size effects in metallic superlattice systems
Clean metallic superlattice systems composed of alternating layers of
superconducting and normal materials are considered, particularly aspects of
the proximity effect as it affects the critical temperature. A simple model is
used to address the question of when a finite--sized system theoretically
approximates well a true infinite superlattice. The methods used in the
analysis afford some tests of the approximation used that the pair amplitude of
the Cooper pairs is constant over a superconducting region. We also use these
methods to construct a model of a single superconducting layer which intends to
incorporate a more realistic form of the pair amplitude than a simple constant.Comment: 16 ReVTeX pages + 12 PostScript figures encoded with uufile
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