Shot noise in a strange metal.

Strange-metal behavior has been observed in materials ranging from high-temperature superconductors to heavy fermion metals. In conventional metals, current is carried by quasiparticles; although it has been suggested that quasiparticles are absent in strange metals, direct experimental evidence is lacking. We measured shot noise to probe the granularity of the current-carrying excitations in nanowires of the heavy fermion strange metal YbRh2Si2. When compared with conventional metals, shot noise in these nanowires is strongly suppressed. This suppression cannot be attributed to either electron-phonon or electron-electron interactions in a Fermi liquid, which suggests that the current is not carried by well-defined quasiparticles in the strange-metal regime that we probed. Our work sets the stage for similar studies of other strange metals.

ScRu2B3 and Sc2RuB6: Borides Featuring a 2D Infinite Boron Clustering.

Two borides, ScRu2B3 and Sc2RuB6, were obtained by argon-arc melting of the elements followed by annealing at 800 °C. ScRu2B3 exhibits a new structure type with the space group Cmcm (a = 3.0195(2) Å, b = 15.4056(8) Å, c = 5.4492(3) Å; single crystal X-ray data; RF2 = 0.0105). Sc2RuB6 adopts the Y2ReB6-type structure (space group Pbam; a = 8.8545(2) Å, b = 11.1620(3) Å, c = 3.4760(1) Å; single crystal X-ray data; RF2 = 0.0185). ScRu2B3 displays an unusual intergrowth of CeCo3B2- and AlB2-related slabs; a striking feature is a boat configuration of puckered boron hexagons within infinite graphite like boron layers (63 nets). Sc2RuB6 presents two-dimensional planar nets of condensed boron pentagons, hexagons, and heptagons sandwiched between metal layers. In Sc/Y substituted Y2ReB6-type, Y atoms are distributed exclusively inside the boron heptagons. Exploration of the Sc-Ru-B system at 800 °C including binary boundaries employing EPMA and powder X-ray diffraction technique furthermore rules out the existence of previously reported "ScRuB4" but confirms the formation and crystal structure of Sc2Ru5B4. ScRu4B4 forms in cast alloys (LuRu4B4-type structure; space group I41/acd (No. 142), a = 7.3543(2) Å, c = 14.92137(8) Å). Cell parameters and atomic coordinates have been refined for ScRu2B3, Sc2RuB6, and ScRu4B4 in the scope of the generalized gradient approximation. Ab initio electronic structure calculations indicate a moderate electronic density of states at the Fermi level situated near the upper edge of essentially filled d-bands. Electrical resistivity measurements characterize ScRu2B3 and Sc2RuB6 as metals in concord with electronic band structure calculations.

Th7 Fe3 -Type Related Structures in Pd(Pt)-Cu-B Systems: Pd6 CuB3 -A New Structure Type for Borides.

A new member of the series of Th7 Fe3 -type derivative structures, h-(Pd0.86 Cu0.14 )7 B3 (≡Pd6.02 Cu0.98 B3 , unique structure type Pd6 CuB3 , space group P63 cm, a=12.9426(9) Å, c=4.8697(4) Å, single-crystal X-ray diffraction (XRD) data) was obtained from as cast alloys and alloys annealed at 600-650 °C. Further substitution of Cu by Pd led to formation of a Mn7 C3 -type structure, o-(Pd0.93 Cu0.07 )7 B3 (≡Pd6.51 Cu0.49 B3 , space group Pnma, a=4.8971(2) Å, b=7.5353(3) Å, c=12.9743(6) Å, single-crystal XRD). Isotypic LT h-(Pt0.70 Cu0.30 )7 B3 (≡Pt4.90 Cu2.10 B3 ) was observed in the Pt-Cu-B system as a low-temperature (LT) phase (T≤600 °C) (powder XRD), whereas the Th7 Fe3 -type (high-temperature (HT) h-(Pt0.73 Cu0.27 )7 B3 ≡Pt5.11 Cu1.89 B3 , space group P63 mc, a=7.4671(1) Å, c=4.9039(1) Å, powder XRD) proved to be stable at high temperature. The three structures are built of columns of face connected metal octahedra and columns of metal tetrahedra alternatingly fused by common faces and vertices. Boron atoms are found in trigonal prisms formed by metal atoms. The volumes of the three new Th7 Fe3 -type derivative borides relate as 1:2:3. Superconductivity was discovered for Pt4.9 Cu2.1 B3 (Pd6 CuB3 -type) and Pt5.1 Cu1.9 B3 (Th7 Fe3 -type) below 0.67 and 0.66 K, respectively. Despite the close value of the transition temperature the values of the upper critical field at 0 K differ as 0.37 T and 0.27 T for the two compounds.

Mechanism of Rare Earth Incorporation and Crystal Growth of Rare Earth Containing Type-I Clathrates.

Type-I clathrates possess extremely low thermal conductivities, a property that makes them promising materials for thermoelectric applications. The incorporation of cerium into one such clathrate has recently been shown to lead to a drastic enhancement of the thermopower, another property determining the thermoelectric efficiency. Here we explore the mechanism of the incorporation of rare earth elements into type-I clathrates. Our investigation of the crystal growth and the composition of the phase Ba8-x RE x TM y Si46-y (RE = rare earth element; TM = Au, Pd, Pt) reveals that the RE content x is mainly governed by two factors, the free cage space and the electron balance.

Pt-B System Revisited: Pt2B, a New Structure Type of Binary Borides. Ternary WAl12-Type Derivative Borides.

On the basis of a detailed study applying X-ray single-crystal and powder diffraction, differential scanning calorimetry, and scanning electron microscopy analysis, it was possible to resolve existing uncertainties in the Pt-rich section (≥65 atom % Pt) of the binary Pt-B phase diagram above 600 °C. The formation of a unique structure has been observed for Pt2B [X-ray single-crystal data: space group C2/m, a = 1.62717(11) nm, b = 0.32788(2) nm, c = 0.44200(3) nm, ß = 104.401(4)°, RF2 = 0.030]. Within the homogeneity range of "Pt3B", X-ray powder diffraction phase analysis prompted two structural modifications as a function of temperature. The crystal structure of "hT-Pt3B" complies with the hitherto reported structure of anti-MoS2 [space group P63/mmc, a = 0.279377(2) nm, c = 1.04895(1) nm, RF = 0.075, RI = 0.090]. The structure of the new "[Formula: see text]T-Pt3B" is still unknown. The formation of previously reported Pt∼4B has not been confirmed from binary samples. Exploration of the Pt-rich section of the Pt-Cu-B system at 600 °C revealed a new ternary compound, Pt12CuB6-y [X-ray single-crystal data: space group Im3̅, a = 0.75790(2) nm, y = 3, RF2 = 0.0129], which exhibits the filled WAl12-type structure accommodating boron in the interstitial trigonal-prismatic site 12e. The isotypic platinum-aluminum-boride was synthesized and studied. The solubility of copper in binary platinum borides has been found to attain ∼7 atom % Cu for Pt2B but to be insignificant for "[Formula: see text]T-Pt3B". The architecture of the new Pt2B structure combines puckered layers of boron-filled and empty [Pt6] octahedra (anti-CaCl2-type fragment) alternating along the x axis with a double layer of boron-semifilled [Pt6] trigonal prisms interbedded with a layer of empty tetrahedra and tetragonal pyramids (B-deficient α-T[Formula: see text]I fragment). Assuming boron vacancies ordering (space group R3), the Pt12CuB6-y structure exhibits serpentine-like columns of edge-connected boron-filled [Pt6] trigonal prisms running infinitely along the z axis and embedding the icosahedrally coordinated Cu atom. Pt2B, (Pt1-yCuy)2B (y = 0.045), and Pt12CuB6-y (y = 3) behave metallically, as revealed by temperature-dependent electrical resistivity measurements.

Multiband Transport in CoSb3 Prepared by Rapid Solidification.

Nano-grained CoSb3 was prepared by melt-spinning and subsequent spark plasma sintering. The phonon thermal conductivity of skutterudites is known to be sensitive to the kind and the amount of guest atoms. Thus, unfilled CoSb3 can serve as model compound to study the impact of a nanostructure on the thermoelectric properties, especially the phonon thermal conductivity. Therefore, a series of materials was prepared differing only by the cooling speed during the quenching procedure. In contrast to clathrates, the microstructure of meltspun CoSb3 was found to be sensitive to the cooling speed. Although the phonon thermal conductivity, studied by means of Flash and 3ω measurements, was found to be correlated with the grain size, the bulk density of the sintered materials had an even stronger impact. Interestingly, the reduced bulk density did not result in an increased electrical resistivity. The influence of Sb and CoSb2 as foreign phase on the electronic properties of CoSb3 was revealed by a multi-band Hall effect analysis. While CoSb2 increases the charge carrier density, the influence of the highly mobile charge carriers introduced by elemental Sb on the thermoelectric properties of the composite offer an interesting perspective for the preparation of efficient thermoelectric composite materials.