85 research outputs found
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction across a tunneling junction out of equilibrium
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic
- spin impurities across a tunneling junction is studied when the system
is driven out of equilibrium through biasing the junction. The nonequilibrium
situation is handled with the Keldysh time-loop perturbation formalism in
conjunction with appropriate coupling methods for tunneling systems due to
Caroli and Feuchtwang. We find that the presence of a nonequilibrium bias
across the junction leads to an interference of several fundamental
oscillations, such that in this tunneling geometry, it is possible to tune the
interaction between ferromagnetic and antiferromagnetic coupling at a fixed
impurity configuration, simply by changing the bias across the junction.
Furthermore, it is shown that the range of the RKKY interaction is altered out
of equilibrium, such that in particular the interaction energy between two
slabs of spins scales extensively with the thickness of the slabs in the
presence of an applied bias.Comment: 38 pages revtex preprint; 5 postscript figures; submitted to Phys.
Rev.
Time-Dependent Partition-Free Approach in Resonant Tunneling Systems
An extended Keldysh formalism, well suited to properly take into account the
initial correlations, is used in order to deal with the time-dependent current
response of a resonant tunneling system. We use a \textit{partition-free}
approach by Cini in which the whole system is in equilibrium before an external
bias is switched on. No fictitious partitions are used. Besides the
steady-state responses one can also calculate physical dynamical responses. In
the noninteracting case we clarify under what circumstances a steady-state
current develops and compare our result with the one obtained in the
partitioned scheme. We prove a Theorem of asymptotic Equivalence between the
two schemes for arbitrary time-dependent disturbances. We also show that the
steady-state current is independent of the history of the external perturbation
(Memory Loss Theorem). In the so called wide-band limit an analytic result for
the time-dependent current is obtained. In the interacting case we propose an
exact non-equilibrium Green function approach based on Time Dependent Density
Functional Theory. The equations are no more difficult than an ordinary Mean
Field treatment. We show how the scattering-state scheme by Lang follows from
our formulation. An exact formula for the steady-state current of an arbitrary
interacting resonant tunneling system is obtained. As an example the
time-dependent current response is calculated in the Random Phase
Approximation.Comment: final version, 18 pages, 9 figure
Magneto-Coulomb Oscillation in Ferromagnetic Single Electron Transistors
The mechanism of the magneto-Coulomb oscillation in ferromagnetic single
electron transistors (SET's) is theoretically considered. Variations in the
chemical potentials of the conduction electrons in the ferromagnetic island
electrode and the ferromagnetic lead electrodes in magnetic fields cause
changes in the free energy of the island electrode of the SET. Experimental
results of the magneto-Coulomb oscillation in a Ni/Co/Ni ferromagnetic SET are
presented and discussed. Possible applications of this phenomenon are also
discussed.Comment: 24 pages Latex, 5 figures in GIF files, style files included. Revised
version: some errors are corrected and further discussions are added. To be
published in J. Phys. Soc. Jpn. Vol.67 (1998) No.
Моделі процесів захисту цілісності інформаційних об’єктів з використанням коду умовних лишків. Алгоритм нулізації
The models of processes of defense of integrity of information’s holding object with application of code of conditional tailings which provide high probabilities of exposure of violations of integrity and correction of the exposed curvatures are examined
‘To be one’s own boss’:Exceptional entrepreneurs and products that sell themselves in urban Poland
Collaboration and knowledge exchange between scholars in Britain and the empire, 1830–1914
In recent years there has been a growing interest among historians in the British Empire as a space of knowledge production and circulation. Much of this work assumes that scholarly cooperation and collaboration between individuals and institutions within the Empire had the effect (and often also the aim) of strengthening both imperial ties and the idea of empire. This chapter argues, however, that many examples of scholarly travel, exchange, and collaboration were undertaken with very different goals in mind. In particular, it highlights the continuing importance of an ideal of scientific internationalism, which stressed the benefits of scholarship for the whole of humanity and prioritized the needs and goals of individual academic and scientific disciplines. As the chapter shows, some scholars even went on to develop nuanced critiques of the imperial project while using the very structures of empire to further their own individual, disciplinary and institutional goals
Theory of spin-polarized transport in photoexcited semiconductor/ferromagnet tunnel junctions
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