Roman Gumeniuk

Superconductivity in the Platinum Germanides MPt4Ge12 (M = Rare-Earth or Alkaline-Earth Metal) with Filled Skutterudite Structure

New germanium-platinum compounds with the filled-skutterudite crystal structure were synthesized. The crystal structure and composition were investigated by x-ray diffraction and microprobe analysis. Magnetic susceptibility, specific heat, and electrical resistivity measurements evidence superconductivity in LaPt4Ge12 and PrPt4Ge12 below 8.3 K. The parameters of the normal and superconducting states were established. Strong coupling and a crystal electric field singlet ground state is found for the Pr compound. Electronic structure calculations show a large density of states at the Fermi level. Similar behavior with lower Tc was observed for SrPt4Ge12 and BaPt4Ge12.

Valence fluctuations of europium in the boride Eu4Pd29+xB8

We synthesized a high-quality sample of the boride Eu4Pd(29+x)B8 (x  =  0.76) and studied its structural and physical properties. Its tetragonal structure was solved by direct methods and confirmed to belong to the Eu4Pd29B8 type. All studied physical properties indicate a valence fluctuating Eu state, with a valence decreasing continuously from about 2.9 at 5 K to 2.7 at 300 K. Maxima in the T dependence of the susceptibility and thermopower at around 135 K and 120 K, respectively, indicate a valence fluctuation energy scale on the order of 300 K. Analysis of the magnetic susceptibility evidences some inconsistencies when using the ionic interconfigurational fluctuation (ICF) model, thus suggesting a stronger relevance of hybridization between 4f and valence electrons compared to standard valence-fluctuating Eu systems.

Superfluid Density and Energy Gap Function of Superconducting PrPt4Ge12

The filled skutterudite superconductor PrPt4Ge12 was studied in muon-spin rotation (muSR), specific heat, and electrical resistivity experiments. The continuous increase of the superfluid density with decreasing temperature and the dependence of the magnetic penetration depth lambda on the magnetic field obtained by means of muSR, as well as the observation of a T3 dependence of the electronic specific heat indicate the presence of pointlike nodes in the superconducting energy gap. The gap and the specific heat are found to be well described by two models with point nodes, similar to results obtained for the unconventional heavy fermion skutterudite superconductor PrOs4Sb12.

Substitution-induced superconductivity in SrFe 2 − x Ru x As 2 ( 0 ≤ x ≤ 2 )

The magnetism in SrFe2As2 can be suppressed by electron doping through a small substitution of Fe by Co or Ni, giving way to superconductivity. We demonstrate that a massive substitution of Fe by isovalent ruthenium similarly suppresses the magnetic ordering in SrFe2-xRuxAs2 and leads to bulk superconductivity for 0.6 <= x <= 0.8. Magnetization, electrical resistivity, and specific heat data show Tc up to approx 20K. Detailed structural investigations reveal a strong decrease of the lattice parameter ratio c/a with increasing x. DFT band structure calculations are in line with the observation that the magnetic order in SrFe2-xRuxAs2 is only destabilized for large x.

Weak interband-coupling superconductivity in the filled skutterudite LaPt4Ge12

The superconducting pairing state of LaPt

Synthesis, crystal structure and properties of the new superconductors TaRuB and NbOsB

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Filled platinum germanium skutterudites MPt4Ge12 (M = Sr, Ba, La—Nd, Sm, Eu): crystal structure and chemical bonding

Ge

Electronic structure and thermodynamic properties of Ce3Rh4Sn13 and La3Rh4Sn13

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Structural transformation with "negative volume expansion": Chemical bonding and physical behavior of TiGePt

is studied by measuring the magnetic penetration depth

Electronic structure of SrPt4Ge12: Combined photoelectron spectroscopy and band structure study

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