The isotope effect in thermal diffusion (Soret effect) of benzene+cyclohexane mixtures has been investigated by a holographic grating technique. The Soret coefficient can be split into additive contributions. One contribution, the isotope effect, stems from the differences of both mass and moment of inertia, and is independent of composition. An additional "chemical" contribution depends on concentration and even changes its sign at a benzene mole fraction x(benz) approximately 0.7. The mass effect is in agreement with molecular dynamics calculations: the heavier component migrates to the cold side.

An experimental study of the proximity effect of superconductor-normal metal films with the help of lowtemperature scanning tunneling spectroscopy is reported. The behaviors of bilayers of the noble metals gold and silver in contact with the superconductor aluminum are compared for various thicknesses of the normal metal. Although the normal conducting properties of Au and Ag are very similar to each other, the measured differential conductance spectra from which the quasiparticle density of states is deduced differ markedly. While the behavior of the Al/Ag system follows the quasiclassical theory of the proximity effect for diffusive systems, differences exist for the Al/Au system. The absolute value of the induced minigap in Au is larger than predicted by theory, and its suppression with increasing temperature is weaker. These observations are quantitatively accounted for by including a finite interaction parameter for Au of (N 0 V ) Au = 0.10 ± 0.03. The third investigated metal is palladium, which is close to ferromagnetism. The method presented here enables one to detect small superconducting correlations by investigating a spectroscopic property rather than the supercurrent or the critical temperature.

We present a simple design for a very-low temperature STM for the investigation of mesoscopic superconductors. The nonmagnetic microscope operates in a conventional MOTIVATIONUp to now only a small number of scanning tunnelling microscopes (STM) world-wide are operating at temperatures below 1 K, in high magnetic fields, and achieve high energy resolution E < 1 mV. Some of them combine UHV and very low temperatures 1-5 while other designs operate in conventional cryostats. 6-8 The STMs for non-UHV conditions are mostly specialized instruments for investigating heavy fermion superconductors 9 or the spatial dependence of the superconducting proximity effect. [10][11][12] However, a compact STM that combines very low temperatures, operation in magnetic field, and very high energy resolution with robustness, versatility and easy handling is still lacking. Our new setup that is described in the present article fulfills these requirements. It is very small, matching with most commercial low-temperature facilities, does not require elaborate vibration damping and uses only the very modest amount of seven cables. Furthermore, it is already designed for lower temperatures than presented here, is in principle UHV compatible and can be combined with more complex positioning systems. The special physical project, for which purpose our STM was designed, is to investigate the 525 0022-2291/07/0500-0525/0