The in-plane resistivity, in-plane absolute thermopower, and upper critical field measurements are reported for single-crystal samples of YNi 2 B 2 C and LuNi 2 B 2 C superconductors. The in-plane resistivity shows metallic behavior and varies approximately linearly with temperature near room temperature ͑RT͒ but shows nearly quadratic behavior in temperature at low temperatures. The YNi 2 B 2 C and LuNi 2 B 2 C single-crystal samples exhibit large transverse magnetoresistance ͑Ϸ6-8 % at 45 kOe͒ in the ab plane. The absolute thermopower S(T) is negative from RT to the superconducting transition temperature T c. Its magnitude at RT is a few times of the value for a typical good metal. S(T) is approximately linear in temperature between Ϸ150 K and RT. Extrapolation to Tϭ0 gives large intercepts ͑few V/K͒ for both samples suggesting the presence of a much larger ''knee'' than would be expected from electron-phonon interaction renormalization effects. The upper critical fields for H parallel and perpendicular to the c axis and the superconducting parameters derived from it do not show any anisotropy for the YNi 2 B 2 C single-crystal samples in agreement with magnetization and torque magnetometry measurements, but a small anisotropy is observed for the LuNi 2 B 2 C single crystals. The analysis shows that these are moderately strong-coupling type-II superconductors ͑similar to the A-15 com-pounds͒ with a value of the electron-phonon coupling parameter ͑0͒ approximately equal to 1.2 for YNi 2 B 2 C and 1.0 for LuNi 2 B 2 C, the Ginzburg-Landau coherence length ͑0͒ approximately equal to 70 Å, and H c2 (0)ϳ60-70 kOe. The temperature dependence of the upper critical field shows a positive curvature near T c in disagreement with the Werthamer, Helfand, Hohenberg, and Maki ͑WHHM͒ theory but in agreement with a recent solution of the Gor'kov equation using a basis formed by Landau levels ͑Bahcall͒; however, the data show a severe disagreement between the observed low-temperature behavior of H c2 (T) and that predicted either by WHHM or Bahcall's expressions. ͓S0163-1829͑97͒06413-8͔

The in-plane resistivity and magnetization measurements as a function of the magnitude and direction of the magnetic field and the temperature are reported for single-crystal samples of the HoNi 2 B 2 C magnetic superconductor. Features corresponding to several distinct magnetic phases and the coexistence of superconductivity with two of the magnetic phases are observed. Contrary to previous measurements for polycrystalline samples, reentrant superconductivity is not observed in the absence of a field for these samples. The measurements indicate an extremely rich interplay between superconductivity and different magnetic structures that can be influenced by field, temperature, and current. The results correlate quantitatively with and complement previous determinations of the magnetic phase diagram and qualitatively with determinations of the superconducting phases by measurements of the single-crystal magnetization and heat capacity. HoNi 2 B 2 C is highly anisotropic, and phase diagrams for the field along the ͑100͒ and ͑001͒ directions are presented.

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We report diamagnetic levitation of droplets and/or particles of pico-femtoliter volume and demonstrate their on-chip storage and high precision manipulation (translation, merging, assembling and rotation). We also demonstrate a levitation based microfluidic processor to process droplets/particles with up to a billion times smaller volume than in typical microfluidic devices. The levitated particles can be positioned with up to 300 nm accuracy and precisely rotated and assembled, providing a different physical approach for Micro-Electro-Mechanical-Systems. Force can be applied to the droplets/particles via magnetic, electric and gravitational fields with up to femto Newton accuracy, and potential energy can be controlled with up to 0.2 zepto J (0.05 T k B) precision, thus providing experimental tools for fundamental studies.

Point contacts are used to investigate the anisotropy of the superconducting energy gap in LuNi2B2C in the ab plane and along the c axis. It is shown that the experimental curves should be described assuming that the superconducting gap is non-uniformly distributed over the Fermi surface. The largest and the smallest gaps have been estimated by two-gap fitting models. It is found that the largest contribution to the point-contact conductivity in the c direction is made by a smaller gap and, in the ab plane by a larger gap. The deviation from the one-gap BCS model is pronounced in the temperature dependence of the gap in both directions. The temperature range, where the deviation occurs, is for the c direction approximately 1.5 times more than in the ab plane. The Γ parameter, allowing quantitatively estimate the gap anisotropy by one-gap fitting, in c direction is also about 1.5 times greater than in the ab plane. Since it is impossible to describe satisfactorily such gap distribution either by the one-or two-gap models, a continuous, dual-maxima model of gap distribution over the Fermi surface should be used to describe superconductivity in this material.