Dynamical Origin of Decoherence in Clasically Chaotic Systems

The decay of the overlap between a wave packet evolved with a Hamiltonian H and the same state evolved with H}+$\Sigma$ serves as a measure of the decoherence time $\tau_{\phi}$. Recent experimental and analytical evidence on classically chaotic systems suggest that, under certain conditions, $\tau_{\phi}$ depends on H but not on $\Sigma$. By solving numerically a Hamiltonian model we find evidence of that property provided that the system shows a Wigner-Dyson spectrum (which defines quantum chaos) and the perturbation exceeds a crytical value defined by the parametric correlations of the spectra.Comment: Typos corrected, published versio

Quantum interference due to crossed Andreev reflection in a d-wave superconductor with two nano-contacts

The crossed Andreev reflection in a hybrid nanostructure consisting of a d-wave superconductor and two quantum wires is theoretically studied. When the (110) oriented surface of the superconductor is in contact with the wires parallel and placed close to each other, the Andreev bound state is formed by the crossed Andreev reflection. The conductance has two resonance peaks well below the gap structure in the case of tunnel contacts. These peaks originate from the bonding and antibonding Andreev bound states of hole wave functions.Comment: 4 pages, 3 figure

The Unions of the Families in Wielkopolska

In the begining of the 20th century in Poland land aristocracy had founded unions of the families. In Wielkopolska which was a part of Germany in this time, four families (Chłapowski, Żółtowski, Moszczeński i Szuman) founded their unions to the begining of the Great War. Every of this union had the statutes and funds for their activity. Membership had laws and duties. Ideas of union were consolidation of family, material help for member who needed it, helping young members to get the education and upbringing of young people. Unions of the families performed also different functions of family. I used achievements of Poznań School of Family Reserch to show how these organisations realised them in micro and macro structure of Polish society

Peak Values of Conductivity in Integer and Fractional Quantum Hall Effect

The diagonal conductivity $\sigma_{xx}$ was measured in the Corbino geometry in both integer and fractional quantum Hall effect (QHE). We find that peak values of $\sigma_{xx}$ are approximately equal for transitions in a wide range of integer filling factors $3<\nu<16$, as expected in scaling theories of QHE. This fact allows us to compare peak values in the integer and fractional regimes within the framework of the law of corresponding states.Comment: 8 pages (revtex format), 3 postscript figure

Momentum noise in a quantum point contact

Ballistic electrons flowing through a constriction can transfer momentum to the lattice and excite a vibration of a free-standing conductor. We show (both numerically and analytically) that the electromechanical noise power P does not vanish on the plateaus of quantized conductance -- in contrast to the current noise. The dependence of $P$ on the constriction width can be oscillatory or stepwise, depending on the geometry. The stepwise increase amounts to an approximate quantization of momentum noise.Comment: 4 pages including 4 figure

Electron Standing Wave Formation in Atomic Wires

Using the Landauer formulation of transport theory and tight binding models of the electronic structure, we study electron transport through atomic wires that form 1D constrictions between pairs of metallic nano-contacts. Our results are interpreted in terms of electron standing waves formed in the atomic wires due to interference of electron waves reflected at the ends of the atomic constrictions. We explore the influence of the chemistry of the atomic wire-metal contact interfaces on these standing waves and the associated transport resonances by considering two types of atomic wires: gold wires attached to gold contacts and carbon wires attached to gold contacts. We find that the conductance of the gold wires is roughly $1 G_0 = 2 e^2/h$ for the wire lengths studied, in agreement with experiments. By contrast, for the carbon wires the conductance is found to oscillate strongly as the number of atoms in the wire varies, the odd numbered chains being more conductive than the even numbered ones, in agreement with previous theoretical work that was based on a different model of the carbon wire and metal contacts.Comment: 14 pages, includes 6 figure

Random-Matrix Theory of Parametric Correlations in the Spectra of Disordered Metals and Chaotic Billiards

We study the response to an external perturbation of the energy levels of a disordered metallic particle, by means of the Brownian-motion model introduced by Dyson in the theory of random matrices, and reproduce the results of a recent microscopic theory of Altshuler, Simons, and Szafer. This establishes the validity of Dyson's basic assumption, that parametric correlations in the energy spectrum are dominated by level repulsion, and therefore solely dependent on the symmetry of the hamiltonian. ***Submitted to Physica A.****Comment: 24 pages, REVTeX-3.0, INLO-PUB-931028

Rate of energy absorption by a closed ballistic ring

We make a distinction between the spectroscopic and the mesoscopic conductance of closed systems. We show that the latter is not simply related to the Landauer conductance of the corresponding open system. A new ingredient in the theory is related to the non-universal structure of the perturbation matrix which is generic for quantum chaotic systems. These structures may created bottlenecks that suppress the diffusion in energy space, and hence the rate of energy absorption. The resulting effect is not merely quantitative: For a ring-dot system we find that a smaller Landauer conductance implies a smaller spectroscopic conductance, while the mesoscopic conductance increases. Our considerations open the way towards a realistic theory of dissipation in closed mesoscopic ballistic devices.Comment: 18 pages, 5 figures, published version with updated ref

Magneto-electrical subbands of freely suspended quantum point contacts

We present a versatile design of freely suspended quantum point contacts with particular large one-dimensional subband quantization energies of up to 10meV. The nanoscale bridges embedding a two-dimensional electron system are fabricated from AlGaAs/GaAs heterostructures by electron-beam lithography and etching techniques. Narrow constrictions define quantum point contacts that are capacitively controlled via local in-plane side gates. Employing transport spectroscopy, we investigate the transition from electrostatic subbands to Landau-quantization in a perpendicular magnetic field. The large subband quantization energies allow us to utilize a wide magnetic field range and thereby observe a large exchange splitted spin-gap of the two lowest Landau-levels