Signatures of modulated pair interaction in cuprate superconductors

Recent low-temperature scanning tunnelling spectroscopy experiments on the surface of BSCCO-2212 have revealed a strong positive correlation between the position of localized resonances at -960 meV identified with interstitial oxygen dopants and the size of the local spectral gap. We review efforts to understand these correlations within a model where the dopants modulate the pair interaction on an atomic scale. We provide further evidence for this model by comparing the correlations between the dopants and the local density of states with experimental results.Comment: 4 pages, 2 figures, submitted to M2S-HTSC VIII, Dresden 200

Quasilinear spin voltage profiles in spin thermoelectrics

Recent experiments show that spin thermoelectrics is a promising approach to generate spin voltages. While spin chemical potentials are often limited to a surface layer of the order of the spin diffusion length, we show that thermoelectrically induced spin chemical potentials can extend much further in itinerant ferromagnets with paramagnetic impurities. In some cases, conservation laws, e.g., for a combination of spin and heat currents, give rise to a linear spin voltage profile. More generally, we find quasilinear profiles involving a spin thermoelectric length scale which far exceeds the spin diffusion length.Comment: 4+ page

Imperfect nesting and Peierls instability for a two-dimensional tight-binding model

Based on a half-filled two-dimensional tight-binding model with nearest-neighbour and next nearest-neighbour hopping the effect of imperfect Fermi surface nesting on the Peierls instability is studied at zero temperature. Two dimerization patterns corresponding to a phonon vector $(\pi, \pi)$ are considered. It is found that the Peierls instability will be suppressed with an increase of next nearest-neighbour hopping which characterizes the nesting deviation. First and second order transitions to a homogeneous state are possible. The competition between the two dimerized states is discussed.Comment: 17 pages, 10 eps figure

Anomalous Hall effect in a two dimensional electron gas with magnetic impurities

Magnetic impurities play an important role in many spintronics-related materials. Motivated by this fact, we study the anomalous Hall effect in the presence of magnetic impurities, focusing on two-dimensional electron systems with Rashba spin-orbit coupling. We find a highly nonlinear dependence on the impurity polarization, including possible sign changes. At small impurity magnetizations, this is a consequence of the remarkable result that the linear term is independent of the spin-orbit coupling strength. Near saturation of the impurity spins, the anomalous Hall conductivity can be resonantly enhanced, due to interference between potential and magnetic scattering.Comment: 5 pages, 3 figure

Microwave conductivity of d-wave superconductors with extended impurities

We investigate the influence of extended scatterers on the finite temperature and finite frequency microwave conductivity of d-wave superconductors. For this purpose we generalize a previous treatment by Durst and Lee, which is based on a nodal approximation of the quasiparticle excitations and scattering processes, and apply it to the analysis of experimental spectra of YBCO-123 and BSCCO-2212. For YBCO, we find that accounting for a slight spatial extension of the strong scattering in-plane defects improves the fit of the low temperature microwave conductivity to experiment. With respect to BSCCO we conclude that it is necessary to include a large concentration of weak-to-intermediate strength extended scatterers, which we attribute to the out-of plane disorder introduced by doping. These findings for BSCCO are consistent with similar analyses of the normal state ARPES spectra and of STM spectra in the superconducting state, where an enhanced forward scattering has been inferred as well.Comment: 10 pages, 11 figure

Dopant-modulated pair interaction in cuprate superconductors

Comparison of recent experimental STM data with single-impurity and many-impurity Bogoliubov-de Gennes calculations strongly suggests that random out-of-plane dopant atoms in cuprates modulate the pair interaction locally. This type of disorder is crucial to understanding the nanoscale electronic structure inhomogeneity observed in BSCCO-2212, and can reproduce observed correlations between the positions of impurity atoms and various aspects of the local density of states such as the gap magnitude and the height of the coherence peaks. Our results imply that each dopant atom modulates the pair interaction on a length scale of order one lattice constant.Comment: 5 pages, 4 figure

Andreev states near short-ranged pairing potential impurities

We study Andreev states near atomic scale modulations in the pairing potential in both $s$- and d-wave superconductors with short coherence lengths. For a moderate reduction of the local gap, the states exist only close to the gap edge. If one allows for local sign changes of the order parameter, however, resonances can occur at energies close to the Fermi level. The local density of states (LDOS) around such pairing potential defects strongly resembles the patterns observed by tunneling measurements around Zn impurities in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (BSCCO). We discuss how this phase impurity model of the Zn LDOS pattern can be distinguished from other proposals experimentally.Comment: 4 pages, 4 figure

From debt to discharge: Consumer insolvency proceedings in Austria

In jüngster Zeit haben zwei Gesetzgebungsakte das österreichische Insolvenzrecht erheblich verändert: Zum einen hat die "Gesamtreform des Exekutionsrechts" (GREx) die Schnittstelle zwischen Einzel- und Gesamtvollstreckung entscheidend umgestaltet. Zum anderen hat die Umsetzung der europäischen Restrukturierungs- und Insolvenzrichtlinie die Rahmenbedingungen für die Restschuldbefreiung nicht nur für Unternehmer, sondern auch für Verbraucher verbessert. Dieser Artikel gibt einen detaillierten Überblick über das Verbraucherinsolvenzverfahren in Österreich und geht hierbei auch auf die Tätigkeiten der anerkannten Schuldenberatungsstellen ein.Recently, two legislative acts have significantly changed Austrian insolvency law: Firstly, the overall reform of enforcement law (“Gesamtreform des Exekutionsrechts – GREx”) has drastically altered the interface between individual and general enforcement. And secondly, the implementation of the European Restructuring and Insolvency Directive has improved the framework for debt discharge not only for entrepreneurs but also for consumers. This article provides a detailed overview of the consumer insolvency proceedings in Austria and also addresses the activities of the recognised debt counselling agencies