Core-level binding energy shifts in dilute alloys

Core level binding energy shifts for the element A of a large number of dilute alloys AB have been measured, where the concentration of the dilute component A is 10% or less. The experimental shifts are analysed in terms of alloy heat of formation data, for which we have used Miedema's semi-empirical scheme. Good overall agreement is obtained between the experimental data and the calculated values, encouraging the use of electron spectroscopy for evaluating solution energies of metallic systems.     

Temperature dependence of the hyperfine fields for fluorine in ferromagnetic iron,nickel and gadolinium

The temperature dependence of the magnetic hyperfine fields at the sites of F nuclei implanted into ferromagnetic Fe, Ni and Gd has been studied in the temperature range from 77 K to 670 K. A pulsed proton beam was used to observe the time-differential precession of the 5/2⁺ state in¹⁹F. Deviations from the bulk magnetization were found for Fe and Ni. The damping of the two observed fields in Ni was interpreted in terms of a field distribution caused by an induced radiation damage. The occupation sites for F and possible mechanisms of the anomalous temperature dependence are discussed.     

Giant enhancement of the valence band photoemission intensity in γ-Ce

We have observed a giant enhancement of the Ce valence band emission above the 4d absorption threshold. It is interpreted as being due to autoionization decay following 4d¹⁰4f¹ → 4d⁹4f² transitions. By taking advantage of this effect we have been able to make a determination of the location of the 4f levels in γ-Ce.     

Fluctuating lattice constants of indium under high pressure

Recent high-pressure investigations of elemental In have yielded controversial results. We show that the observed high-pressure face-centered orthorhombic (fco) structure can be explained as an intermediate state between two body-centered tetragonal (bct) structures with different c/a ratios (c/a < square root [2] and c/a > square root [2], respectively). In a pressure range from about 50 to 200 GPa these two bct structures correspond to local minima of the total energy with respect to orthorhombic distortion of the ground-state bct In structure. The fco saddle point represents a tiny barrier and even at low temperatures rapid structural fluctuations should occur. Such a situation has not been identified in any other elemental metal.     

Measuring non-Gaussian fluctuations through incoherent cooper-pair current

We study a Josephson junction (JJ) in the regime of incoherent Cooper-pair tunneling, capacitively coupled to a nonequilibrium noise source. The current-voltage (I-V) characteristics of the JJ are sensitive to the excess voltage fluctuations in the source, and can thus be used for wideband noise detection. Under weak driving, the odd part of the I-V can be related to the second cumulant of noise, whereas the even part is due to the third cumulant. After calibration, one can measure the Fano factors for the noise source, and get information about the frequency dependence of the noise.     

Gap and out-gap breathers in a binary modulated discrete nonlinear Schrödinger model

We consider a modulated discrete nonlinear Schrödinger (DNLS) model with alternating on-site potential, having a linear spectrum with two branches separated by a forbidden gap. Nonlinear localized time-periodic solutions with frequencies in the gap and near the gap -- discrete gap and out-gap breathers (DGBs and DOGBs) -- are investigated. Their linear stability is studied varying the system parameters from the continuous to the anti-continuous limit, and different types of oscillatory and real instabilities are revealed. It is shown, that generally DGBs in infinite modulated DNLS chains with hard (soft) nonlinearity do not possess any oscillatory instabilities for breather frequencies in the lower (upper) half of the gap. Regimes of exchange of stability between symmetric and antisymmetric DGBs are observed, where an increased breather mobility is expected. The transformation from DGBs to DOGBs when the breather frequency enters the linear spectrum is studied, and the general bifurcation picture for DOGBs with tails of different wave numbers is described. Close to the anti-continuous limit, the localized linear eigenmodes and their corresponding eigenfrequencies are calculated analytically for several gap/out-gap breather configurations, yielding explicit proof of their linear stability or instability close to this limit.Received: 31 October 2003, Published online: 17 February 2004PACS: 63.20.Pw Localized modes - 63.20.Ry Anharmonic lattice modes - 42.65.Wi Nonlinear waveguides