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BaNi2As2 is a nonmagnetic analog of the iron pnictide superconductors, and exhibits an incommensurate charge density wave (IC-CDW) and a sizable elastoresistance. In this Letter, phonons in BaNi2As2 associated with the IC-CDW and uniform in-plane lattice distortions are investigated using high-resolution inelastic x-ray scattering. The in-plane transverse acoustic phonons reveal no softening at temperatures where the elastoresistance increases strongly, indicating the latter to be electronically driven. Systematic phonon measurements suggest the IC-CDW occurs in two stages upon cooling: Underdamped phonons first soften to zero energy well above the IC-CDW ordering temperature, then the resulting quasielastic IC-CDW fluctuations gradually slow down and coalesce into the static IC-CDW order. A possible origin for our observations is the IC-CDW in BaNi2As2 being uniaxial, which provides an additional Ising degree of freedom favorable for disordered IC-CDW modulations, and accounts for the elastoresistance through a weak coupling to the lattice.

We report a new quaternary compound, ThV2Si2C, containing V2C square nets that are sandwiched by Si sheets. The compound crystallizes in a CeCr2Si2C-type structure with cell parameters of a = b = 4.1008 Å and c = 5.4150 Å. Magnetic, electrical transport, and specific heat measurements confirm the Pauli paramagnetic metal behavior in ThV2Si2C, concomitant with low magnetoresistance. At temperatures below 2 K, a possible weak superconducting transition is found. First-principles calculations reveal that V-3d orbitals dominate the electronic states at around the Fermi energy. These states predominantly originate from the dx2−y2, dz2, and dyz orbitals, defining the primarily anisotropic nature of conduction within the V2Si2C block. The differences in the orbital-dependent pairing among charge carriers within isomorphic compounds are discussed. [ABSTRACT FROM AUTHOR]

β-ThRhGe, the high-temperature polymorph of ThRhGe, is isostructural to the well-known ferromagnetic superconductor URhGe. However, contrary to URhGe, β-ThRhGe is nonmagnetic and undergoes an incomplete structural phase transition at 244 K, followed by a superconducting transition below 3.36 K. Here we show that the isovalent substitution of Ir for Rh leads to a strong enhancement of superconductivity by suppressing the structural transition. At x = 0.5, where the structural transition disappears, Tc reaches a maximum of 6.88 K. The enhancement of superconductivity is linked to the proximity to a structural quantum critical point at this Ir concentration, as suggested by the analysis of thermodynamic as well as resistivity data. First principles calculations indicate that the Ir doping has little effect on the electronic band dispersion near the Fermi level. β-ThRh1−xIrxGe thus provides an excellent platform to study the interplay between superconductivity and structural quantum criticality in actinide-containing compounds. [ABSTRACT FROM AUTHOR]

We report the superconductivity of a new quaternary compound ThMo2Si2C, synthesized with the arc-melting technique. The compound crystallizes in a tetragonal CeCr2Si2C-type structure with cell parameters of a = 4.2296 Å and c = 5.3571 Å. An interlayer Si-Si covalent bonding is suggested by the atomic distance. The electrical resistivity and magnetic susceptibility measurements indicate a Pauli-paramagnetic metal with dominant electron-electron scattering in the normal-state. Bulk superconductivity at 2.2 K is demonstrated with a dimensionless specific-heat jump of ΔC/γnT = 0.98. The superconducting parameters of the critical magnetic fields, coherence length, penetration depth, and superconducting energy gap are given. [ABSTRACT FROM AUTHOR]

Differently from most of the other 1111-type iron-based superconductors, ThFeAsN itself shows superconductivity at 30 K without antiferromagnetism, even in the absence of chemical doping and other treating. In order to understand its peculiar behavior better, it is necessary to investigate the evolution of the superconducting phase through electron doping. Chemically, Co doping is a more effective way to introduce electrons, as carriers are doped directly into the FeAs planes. It also could provide information on how well the ThFeAsN tolerates in-plane disorder. Here we have substituted Co for Fe to synthesize ThFe1-xCoxAsN. It is found that the superconductivity of ThFeAsN parent compound is quickly suppressed upon Co doping. With a doping amount of), the superconductivity of ThFe1-xCoxAsN vanishes. ThCoAsN has been synthesized and characterized. It shows no superconductivity at 1.8 K. As both its crystal structure and transport behaviour are similar to those of itinerant ferromagnets LaCoAsO and LaCoPO, it is expected that ThCoAsN would be a kind of itinerant ferromagnet. However, until 1.8 K, the expected itinerant ferromagnetism could not be confirmed. The experimental data support that ThCoAsN is a kind of metallic paramagnet above 1.8 K. [ABSTRACT FROM AUTHOR]

A quaternary compound, ThCr 2 Si 2 C, was synthesized by using the arc-melting technique. The compound adopts a tetragonal CeCr 2 Si 2 C-type crystal structure. The electronic resistivity and specific heat data exhibit metallic behavior, while the magnetic susceptibility displays a pronounced broad peak at around 370 K, indicating the antiferromagnetic phase transition. The first-principles calculations suggest A-type antiferromagnetic ordering of the Cr sublattice, which is confirmed by neutron diffraction experiments. By comparing the crystal structure of ThCr 2 Si 2 C with the isostructural Cr-based compounds, the magnetic state of Cr 3d orbital is discussed in terms of the band-filling effects and indirect spin exchange interaction.