The structurally well-defined intermetallic compound PdGa -a highly selective catalyst for the semi-hydrogenation of acetylene -was characterized by Fourier transform infrared spectroscopy (FTIR), in situ X-ray photoelectron spectroscopy (XPS) and in situ Prompt Gamma Activation Analysis (PGAA). A strong modification of the electronic states in PdGa compared to elemental Pd was revealed as well as the complete isolation of the Pd atoms on the surface of PdGa. In situ investigations proved the high stability of the surface, thus excluding segregation phenomena (common for alloys) or sub-surface chemistry involving C and/or H atoms (known for elemental Pd). By suppressing the sub-surface chemistry, the electronic modification as well as the site isolation lead to the high selectivity and long-term stability of PdGa in the semi-hydrogenation of acetylene.

Zero-and longitudinal-field muon-spin-rotation ͑SR͒ experiments were performed on the superconductors PrPt 4 Ge 12 and LaPt 4 Ge 12 . In PrPt 4 Ge 12 below T c a spontaneous magnetization with a temperature variation resembling that of the superfluid density appears. This observation implies time-reversal symmetry ͑TRS͒ breaking in PrPt 4 Ge 12 below T c = 7.9 K. This remarkably high T c for an anomalous superconductor and the weak and gradual change in T c and of the related specific-heat anomaly upon La substitution in La 1−x Pr x Pt 4 Ge 12 suggests that the TRS breaking is due to orbital degrees of freedom of the Cooper pairs.

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We report on results of electrical resistivity and structural investigations on the cubic modification of FeGe under high pressure. The long-wavelength helical order (T C 280 K) is suppressed at a critical pressure p c 19 GPa. An anomaly at T X p and strong deviations from a Fermi-liquid behavior in a wide pressure range above p c suggest that the suppression of T C disagrees with the standard notion of a quantum critical phase transition. The metallic ground state persisting at high pressure can be described by band-structure calculations if zero-point motion is included. The shortest FeGe interatomic distance display discontinuous changes in the pressure dependence close to the T C p phase line.

We report measurements of the London penetration depth ∆λ(T ) and the electronic specific heat Ce(T ) on high-quality single crystals of the filled-skutterudite superconductor PrPt4Ge12 (Tc ≃8K). Both quantities show a weak temperature dependence at T ≪ Tc, following ∆λ ∼ T n (n ≃ 3.2) and Ce/T ∼ T 2.8 . Such temperature dependences deviate from both conventional s-wave type and nodal superconductivity. A detailed analysis indicates that the superfluid density ρs(T ), derived from the penetration depth, as well as the electronic specific heat can be consistently described in terms of a two-gap model, providing strong evidence of multiband superconductivity for PrPt4Ge12. Recently, a series of new skutterudite superconductors with a germanium-platinum framework, i.e., M Pt 4 Ge 12 (M =Sr, Ba, La, Pr), were successfully synthesized [10,11]. Among all the Pr-filled variants, PrPt 4 Ge 12 shows an unexpectedly high transition temperature of T c =7. [19]. However, these experiments were performed on polycrystalline samples at relatively high temperatures, which could not make a clear assertion on the gap symmetry. The reasons underlying such discrepancies of the gap structure in PrPt 4 Ge 12 are not yet clear, and further measurements, in particular those based on high-quality single crystals, are badly needed.In this Letter, we probe the superconducting gap symmetry of PrPt 4 Ge 12 by measuring the London penetration depth ∆λ(T ) and the specific heat C p (T ) of highquality single crystals. Precise measurements of the penetration depth changes at low temperatures show ∆λ ∼ T n with n ≃ 3.2, indicating that PrPt 4 Ge 12 is actually neither a simple BCS nor a nodal superconductor. A detailed analysis of the superfluid density ρ s (T ), converted from λ(T ), and the electronic specific heat C e (T ) provide strong evidence of two-band SC for PrPt 4 Ge 12 .High-quality single crystals of PrPt 4 Ge 12 were synthesized by using multi-step thermal treatments [20]. Powder X-ray diffraction indicates the presence of a small amount of foreign phases. Energy-dispersive Xray (EDX) analysis confirms that all the crystals have a stoichiometric composition and the impurity phases, mainly PtGe 2 and free Ge, are located at the crystal surfaces [20]. In our measurements, the crystals were mechanically polished to get rid of these surface contaminations. Precise measurements of the resonant frequency shift ∆f (T ) were performed by utilizing a tunnel diode oscillator (TDO) based, self-inductance method at an operating frequency of 7 MHz down to about 0.5K