[en] Results of superconducting tunneling spectroscopy experiments performed on two different types of thin film planar junctions of the heavy-fermion compound UPd₂Al₃ are presented. Cross-type junctions consist of the heavy-fermion base electrode, an insulating layer of native surface oxide and a metal counter electrode (Au or Ag). The contact resistance was only weakly temperature dependent down to the superconducting transition. In the superconducting regime a strongly reduced zero bias conductivity indicated the junction being of the superconductor-insulator-normal metal type. The observed tunneling density of states is clearly due to the superconducting energy gap of UPd₂Al₃ and reveals strong deviations from the typical BCS-result. The second type of junction consists of a thick insulater (SiO) covering the UPd₂Al₃ base electrode with a small hole (20 μm x 20 μm) which enables the metal counter electrode to contact the superconductor. The temperature-dependent contact resistance including a step-like reduction at the superconducting transition shows that these junctions are essentially of the superconductor-normal metal type. Their bias dependent conductivity is discussed in the framework of Andreev-reflection supplemented by critical current and heating effects. (orig.)

[en] The temperature dependence of the Hall resistivity of thin epitaxial UPd₂Al₃ films with low defect densities is investigated. It shows a minimum at 6 K for fields up to 12 T. This feature is attributed to the superposition of a coherence-derived low-temperature Hall coefficient and a skew-scattering contribution. Further implications on the Hall effect in the coherence regime of Kondo lattices are discussed

[en] Highly c-axis oriented thin films of the heavy fermion superconductor UPd₂Al₃ were prepared by coevaporation of the constituent elements with independent rate monitoring of three sources in a molecular beam epitaxy system (MBE). Detailed X-ray and reflection high energy electron diffraction (RHEED) studies revealed the well ordered in-plane structure of the films deposited on sapphire substrates with different orientations. Onset of superconductivity was found up to T_c^on = 1.8 K. (Author)

[en] Temperature and angular resolved measurements of the upper critical field B_c2 of UPd₂Al₃ thin films are presented and compared with new theoretical calculations for weak-coupling s- and d-wave superconductors in the clean limit. In order to take account of the observed anisotropy of the initial slopes near T_c, B'_c2 = -4.9 T/K for B parallel c and B'_c2 = -5.8 T/K for B perpendicular to c, and the crossing of the phase boundaries in the temperature dependence of B_c2 near T^* ∼ 0.75T/T_c, the calculations include anisotropic orbital and paramagnetic pair breaking. Recent speculations upon the occurence of a non-uniform superconducting ''Fulde-Ferrell-Larkin-Ovchinnikov''-state are also considered and incorporated in the calculations. In the region around T^* a minimum between B parallel c and B perpendicular to c in the out-of-plane angular dependence of the upper critical field B_c2(θ) is found experimentally. This cannot be explained by an s-wave order parameter and reduces drastically the possible d-wave functions. To explain the overall data, a mixing of s-wave and a particular d-wave order parameter is proposed. (orig.)

[en] The magnetoresistance and the upper critical field of UPd₂Al₃ thin films is presented for magnetic fields parallel and perpendicular to the c-axis of the hexagonal crystal lattice. The magnetoresistance shows a strong anisotropy in the investigated temperature range from 2 to 35K and in magnetic fields up to 12T. The anisotropy of the upper critical field is small with a ratio of B_c2parallelc/B_{c2perpendiculartoc}=1.2 for T→0. The initial slope at T_c seems to be almost isotropic. ((orig.))

[en] Thin films of the heavy-fermion superconductor UPt₃ were deposited on various substrate materials in various orientations by means of a quasi-multilayer sputter process. Strongly (0001)-textured growth of the hexagonal compound was found for a uranium content in the range of 23% to 28% on sapphire (101-bar2), LaAlO₃(111) and SrTiO₃(111) with perfect in-plane order on the latter substrate material. Atomic force microscopy and scanning electron microscopy revealed a Vollmer-Weber-like growth mode resulting in the development of large compressive strain in films on SrTiO₃(111). As a result the electronic transport properties - in particular the temperature dependence of the resistivity - were strongly renormalized. Strong deviations from the typical heavy-fermion characteristics known from UPt₃ bulk samples were found in films on SrTiO₃ with residual resistance ratios ρ(300 K)/ρ₀ up to 930 and a significantly reduced superconducting transition temperature of 130 mK. (author)

[en] First results concerning the E(j) characteristics of thin epitaxial UPd₂Al₃ films as a function of the magnetic field oriented parallel to the film's c-axis are presented. The activation energy for flux creep E_A was extracted from resistive transitions in applied magnetic fields. E_A is found to be temperature independent, but depends linearly on the magnetic field B for B≥1T. The critical current density reaches 6500A/cm² at B=1T and T=0.32K. ((orig.))

[en] Highly c-axis oriented thin films of the heavy fermion superconductor UPd₂Al₃ were prepared by electron-beam coevaporation of the constituent elements in a MBE-system. The phase purity and structural quality of the films deposited on different substrate materials were investigated. For transport measurements the films were patterned by photoresist techniques and etched with diluted nitric acid. Investigations of the normal and superconducting transport properties were performed. The highest superconducting onset reaches 1.8 K. ((orig.))