Semiclassical theory in Andreev billiards: beyond the diagonal approximation

Recently semiclassical approximations have been successfully applied to study the effect of a superconducting lead on the density of states and conductance in ballistic billiards. However, the summation over classical trajectories involved in such theories was carried out using the intuitive picture of Andreev reflection rather than the semiclassical reasoning. We propose a method to calculate the semiclassical sums which allows us to go beyond the diagonal approximation in these problems. In particular, we address the question of whether the off-diagonal corrections could explain the gap in the density of states of a chaotic Andreev billiard.Comment: 11 page

Suppression of Giant Magnetoresistance by a superconducting contact

We predict that current perpendicular to the plane (CPP) giant magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed when one of the contacts is superconducting. This is a consequence of a superconductivity-induced magneto-resistive (SMR) effect, whereby the conductance of the ferromagnetically aligned state is drastically reduced by superconductivity. To demonstrate this effect, we compute the GMR ratio of clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd tight binding Hamiltonian. By analyzing a simpler model with two orbitals per site, we also show that the suppression survives in the presence of elastic scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR

Inbreeding in the White Leghorn Fowl

A study, extending over a 10-year period, has been made of the effect of inbreeding in the White Leghorn breed of domestic fowl. The major object of this investigation was to study the effect of various intensities of inbreeding on the following characters: Fertility, hatchability, viability, days to first egg, egg production, egg size and body size. In the present investigation the degree of inbreeding was, in general, less intense than that from brother and sister or parent and offspring matings. One intensely inbred family, however, with the equivalent of brother and sister mating, was maintained successfully for nine generations. Six more or less distinct families, each with a somewhat different type and intensity of inbreeding but with a similar foundation ancestry, were developed. All individuals were selected primarily on the basis of high hatchability of their eggs, upon general vigor of the individual bird and of the offspring of each pair of birds. Other characters besides vigor and hatchability also were considered whenever practical. The ancestry of all the birds in the present generation of these 6 families may be traced to four males and seven females. One of the four original males (No. 823), however, has a greater degree o£ relationship to the present generation than any of the other foundation birds. This relationship still averages approximately 55 percent, with the lowest degree of relationship being 29 percent and the highest 61 percent. The relationship of the present generation to the other three foundation males does not exceed 5 percent. The relationship between brothers and sisters in the present generation chicks of the separate families ranges from 74 to 94 percent. The average inter-se relationship between the present chicks which are not sibs is above 50 percent. The inbreeding coefficients of the present birds range from 41 percent for the least inbred to 82 percent for the most intensely inbred family. There was no general decrease in percent of eggs fertile as the degree of inbreeding increased ; in fact some inbred families have shown an increase in percent of eggs fertile. There was a slow but gradual decline in the average percent hatchability of fertile eggs set for all inbreds as the inbreeding increased. The average hatchability for all inbreds, however, was in most cases well above 60 percent. In six of the families studied there was no general decrease in hatchability, which demonstrates that it is possible to maintain a reasonably safe level of hatchability under a system of intense inbreeding. There was a significant decrease in the number of days to first egg. The most intensely inbred birds on the average matured sexually 16 days earlier than the birds of the original non-inbred foundation stock. There was a general but not a consistent decrease in number of eggs laid during a given period as the inbreeding increased. An exception was observed for the 70 percent inbred group which compared favorably with the original non-inbred foundation birds in egg production. There was no marked decrease in 200-day egg production for anyone of the six separate families as a result of the inbreeding. The data on egg weight suggest no general decrease or increase in average egg weight as a result of the inbreeding. The results indicate that intensive inbreeding did not decrease materially the growth rate or adult body weight of the birds used in this experiment. With the exception of the 80 percent group, there was no increase in mortality in any of the groups up to 24 weeks of age. The pullet year mortality, however, showed a marked rise for the more intensely inbred birds with the exception of that group of birds having an inbreeding coefficient of 70 percent

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The Surface Roughness and Gloss of Composites

The contrast gloss and the average roughness were measured for four commercial composite filling materials. Using a factorial design, each material was subjected to four available finishing methods. A significant difference was found in the contrast gloss among finishing methods, and a significant linear regression is given which relates the inverse of the contrast gloss to the average roughness. Surface gloss is proposed as playing a major role in the esthetic appearance of composite restorations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68215/2/10.1177_00220345840630051601.pd

Giant Backscattering Peak in Angle-Resolved Andreev Reflection

It is shown analytically and by numerical simulation that the angular distribution of Andreev reflection by a disordered normal-metal -- superconductor junction has a narrow peak at the angle of incidence. The peak is higher than the well-known coherent backscattering peak in the normal state, by a large factor G/G_0 (where G is the conductance of the junction and G_0=2e^2/h). The enhanced backscattering can be detected by means of ballistic point contacts.Comment: Instituut-Lorentz, Leiden, The Netherlands, 4 pages, REVTeX-3.0, 3 figure

Phase coherent transport in hybrid superconducting structures: the case of d-wave superconductors

We examine the effect of d-wave symmetry on zero bias anomalies in normal-superconducting tunnel junctions and phase-periodic conductances in Andreev interferometers. In the presence of d-wave pairing, zero-bias anomalies are suppressed compared with the s-wave case. For Andreev interferometers with aligned islands, the phase-periodic conductance is insensistive to the nature of the pairing, whereas for non-aligned islands, the nature of the zero-phase extremum is reversed.Comment: 10 Pages, Revtex. 11 postscript figures available on reques