Magnetotransport of superconducting Nd2−xCexCuO4+y (NdCeCuO) films is studied in the temperature interval 0.3-30 K. The microscopic theory of the quantum corrections to conductivity, both in the Cooper and in the diffusion channels, qualitatively describes the main features of the experiment including the negative magnetoresistance in the high field limit. Comparison with the model of the field-induced superconductor-insulator transition is included and a crossover between these two theoretical approaches is discussed.

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Quantification of the surface composition of low-work function systems using low-energy noble gas ion scattering is strongly influenced by resonant neutralization. Below a certain threshold in the work function, resonant neutralization to the first excited level of the ion is possible and the neutralization probability of the ions increases exponentially with decreasing work function. We show how to correct for the influence of the work function and perform the quantification using the characteristic velocity method. The discussion and conclusions here are relevant for all ion scattering studies using low-energy noble gas ions on surfaces with a work function below ∼4 eV.

The work function dependence of the neutralization of low-energy He ϩ , Ne ϩ , and Ar ϩ ions was studied by determining the neutralization probability of ions scattered from submonolayer coverages of Ba on W͑110͒ and Re͑0001͒ substrates. At high work functions ͑Ͼ3.5 eV͒, it was found that the dominant neutralization mechanism for noble gas ions with initial energy between 2 and 5 keV scattering from Ba is collision-induced neutralization. The neutralization probability for this mechanism was found to be insensitive to work function changes. We argue that collision-induced neutralization is also the dominant charge transfer process for scattering from other earth-alkali and alkali elements in this energy range, although at lower energies it is expected that Auger neutralization will become important. At work functions below roughly 3.5 eV, resonant neutralization to the first excited level of the noble gas ions occurs in addition to the charge transfer processes operating at high work functions. We show that the additional neutralization at low work functions can be described using resonant charge exchange theory. Due to resonant neutralization, the neutralization probability for noble gas ions increases exponentially with decreasing work function.