Fyzikální ústav Akademie věd ČR

Selected results of department 23

Quantum dot attached to two supercondicting leads

Two quite different worlds meet at the quantum dot attached to two superconducting leads. Quantum dot allows us to follow individual electrons and Cooper pairs. Quantum dot in a superconducting environment allows us to study exotic physical phenomena and simultaneously promises technological applications.   The full text >>

Hydrodynamic Brownian motors

Sorting of very small particles dispersed in a fluid is a crucial problem of microfluidics and nanofluidics. A small pump pushing the fluid back and forth keeps the system very far from equilibrium. We show that combined action of inertial hydrodynamic effects plus Brownian motion leads to rectification of particle flow. We computed the average particle velocity analytically. This velocity is strongly sensitive to particle size, which promises high eficiency of sorting.   The full text >>

Hund's impurities

Iron atoms adsorbed on a platinum surface were probed by the scanning tunneling microscope under changing conditions (changes of temperature, presence or absence of hydrogen). Theoretical analysis of the observed magnetic behavior indicates that these atoms behave as the so-called Hund's impurities. These impurities can be identified as building blocks of one class of high-temperature superconductors.   The full text >>

Isogeometric analysis in electronic structure calculations

Properties and behavior of various, even hypothetical, materials can be predicted via ab-initio electronic structure calculations that can provide all the necessary information : the total energy of the system and its derivatives with respect to appropriate parameters. In case of non-periodic structures, the existing well-established methods for electronic structure calculations either use special bases, predetermining and limiting the shapes of wave functions, or require artificial computationally expensive arrangements, like large supercells.   The full text >>

Transient magnetic tunneling mediated by a molecular bridge

The archetypal molecular bridge – a single level molecular island connected by tunneling junctions to two massive leads – acquires new properties, if the leads are ferromagnetic metals. We have studied transient effects induced by suddenly connecting the leads in the parallel geometry. The tunneling is spin dependent and a local magnetization is formed on the level originally empty. The process depends on the strength U of the local electron-electron interaction and on the structure of the tunneling functions. A model prediction of the time evolution of the transient local magnetization is shown in the figure for reasonable values of U. The incipient coherent oscillations, almost independent on U, are damped. The saturation magnetization is first zero, for U increasing from zero, then negative, i.e. opposite with respect to the magnetization of the leads. At a critical value of U, the saturation magnetization reverts and further depends but weakly on increasing U.   The full text >>

Exchange and spin-orbit induced phenomena in diluted (Ga,Mn)As

A broad range of physical properties (magnetic moments, Curie temperatures, spin-stiffness, residual resistivity, anisotropic magnetoresistance, anomalous Hall effect, and Gilbert damping) of a prototypical spintronics material, namely, epitaxially grown GaMnAs alloys, was determined from first principles. An overall good agreement with recent experiments on well-annealed samples was obtained for all studied quantities. The unique feature of the present study is its complexity and the consistent description of several independent quantities.  The full text >>

Magnetic properties of random FeCo overlayers

The study of magnetic properties of ultrathin random films is important for spintronics applications as well as from the fundamental point of view. The parameter-free determination of the Curie temperature of low-dimensional systems is much more demanding as compared to bulk systems, among other things surface exchange interactions decay with the distance more slowly. As a model study, we investigated electronic structure and thermodynamical properties of Fe and Co overlayers on the fcc-Cu(001) substrate.  The full text >>

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