We report on a systematic study of the structural, magnetic and transport properties of highpurity 1T-VS 2 powder samples prepared under high pressure. The results differ notably from those previously obtained by de-intercalating Li from LiVS 2 . First, no Charge Density Wave (CDW) is found by transmission electron microscopy down to 94 K. Though, ab initio phonon calculations unveil a latent CDW instability driven by an acoustic phonon softening at the wave vector q CDW ≈ (0.21,0.21,0) previously reported in de-intercalated samples. A further indication of latent lattice instability is given by an anomalous expansion of the V-S bond distance at low temperature.Second, infrared optical absorption and electrical resistivity measurements give evidence of non metallic properties, consistent with the observation of no CDW phase. On the other hand, magnetic susceptibility and NMR data suggest the coexistence of localized moments with metallic carriers, in agreement with ab initio band structure calculations. This discrepancy is reconciled by a picture of electron localization induced by disorder or electronic correlations leading to a phase separation of metallic and non-metallic domains in the nm scale. We conclude that 1T-VS 2 is at the verge of a CDW transition and suggest that residual electronic doping in Li de-intercalated samples stabilizes a uniform CDW phase with metallic properties.

Using thermoforging process, dense Ca3Co4O9 (Co349) thermoelectric oxides have been successfully textured. The various parameters influencing the formation of the Co349-textured material have been investigated. The electrical transport measurements show an anisotropy of the resistivity in good agreement with scanning electron microscopy observations. Texture is quantified by neutron-diffraction measurements and correlated to anisotropic resistivity measurements and Seebeck coefficients.

There has been increasing interest in materials where relativistic effects induce non-trivial electronic states with promise for spintronics applications. One example is the splitting of bands with opposite spin chirality produced by the Rashba spin-orbit coupling in asymmetric potentials. Sizable splittings have been hitherto obtained using either heavy elements, where this coupling is intrinsically strong, or large surface electric fields. Here by means of angular resolved photoemission spectroscopy and first-principles calculations, we give evidence of a large Rashba coupling of 0.25 eV Å, leading to a remarkable band splitting up to 0.15 eV with hidden spin-chiral polarization in centrosymmetric BaNiS2. This is explained by a huge staggered crystal field of 1.4 V Å−1, produced by a gliding plane symmetry, that breaks inversion symmetry at the Ni site. This unexpected result in the absence of heavy elements demonstrates an effective mechanism of Rashba coupling amplification that may foster spin-orbit band engineering.

A study of the antiferromagnet CeRh2Si2 by torque, magnetostriction, and transport in pulsed magnetic fields up to 50 Tesla and by thermal expansion in static fields up to 13 Tesla is presented. The magnetic field-temperature phase diagram of CeRh2Si2, where the magnetic field is applied along the easy axis c, is deduced from these measurements. The second-order phase transition temperature TN and the first-order phase transition temperature T1,2 (= 36 K and 26 K at zero-field, respectively) decrease with increasing field. The field-induced antiferromagnetic-to-paramagnetic borderline Hc, which equals 26 T at 1.5 K, goes from first-order at low temperature to secondorder at high temperature. The magnetic field-temperature phase diagram is found to be composed of (at least) three different antiferromagnetic phases. These are separated by the first-order lines H1,2, corresponding to T1,2 at H = 0, and H2,3, which equals 25.5 T at 1.5 K. A maximum of the T 2 -coefficient A of the resistivity is observed at the onset of the high-field polarized regime, which is interpreted as the signature of an enhanced effective mass at the field-induced quantum instability. The magnetic field dependence of the A coefficient in CeRh2Si2 is compared with its pressure dependence, and also with the field dependence of A in the prototypal heavy-fermion system CeRu2Si2.

We report the electrical resistivity, thermoelectric power and magnetization of Sr2−xLaxIrO4 (x = 0 and 0.05) and Sr2Ir1−yRhyO4 (y = 0.05, 0.1 and 0.2) measured below room temperature. In Sr2IrO4, electrons (La substitution) or holes (Rh substitution) can be doped, which lead to a strong decrease of the resistivity. In particular, a nearly-metallic state is realized in the case of Rh doping. The thermoelectric power turns out to be metallic-like for y = 0.2. The presence of a gap in the electronic band structure is robust against these substitutions. From various experimental data, similarities with the 3D charge density wave compound, BaBiO3, are suggested. Nevertheless, rather than a charge density wave, our scenario implies the presence of a spin density wave.

By means of magnetization, specific heat, and muon-spin relaxation measurements, we investigate newly synthesized high-pressure oxidized Cu 0.75 Mo 0.25 Sr 2 YCu 2 O 7.54 , in which overdoping is achieved up to p ∼ 0.46 hole/Cu, well beyond the T c -p superconducting dome of cuprates, where Fermi-liquid behavior is expected. Surprisingly, we find bulk superconductivity with T c = 84 K and superfluid density similar to those of optimally doped YBa 2 Cu 3 O 7−δ . On the other hand, specific heat data display a large electronic contribution at low temperature, comparable to that of nonsuperconducting overdoped La 2−x Sr x CuO 4 . These results point at an unusual high-T c phase with a large fraction of unpaired holes. Further experiments may assess the Fermi-liquid properties of the present phase, which would put into question the paradigm that the high T c of cuprates originates from a non-Fermi-liquid ground state.

International audienceBarium ruthenate Ba4Ru3O10, in which Ru3O12 trimers are connected together to form a checkered twodimensional framework, has been synthesized and its structural, magnetic, and transport properties studied between 300 and 2 K. The paramagnetic to antiferromagnetic transition at TN ≈ 105 K evidenced on the susceptibility curve coincides with an increase of electron localization in transportmeasurements. Thermoelectric power and Hall coefficientmeasurements both exhibit dramatic changes at TN, characteristic of a reconstruction of the bands structure near the Fermi level. No pronounced structural changes are observed at TN in this compound. The magnetic scattering signal on the neutron powder diffraction patterns below TN is weak but can be tentatively modeled with an antiferromagnetic ordering of the spins at both ends of a trimer, the spin of the more symmetric Ru site remaining idle. Crystal field and strong spin-orbit coupling at the Ru4+ site seem to be the key parameters to understand the magnetic state of Ba4Ru3O10

Dirac fermions play a central role in the study of topological phases, for they can generate a variety of exotic states, such as Weyl semimetals and topological insulators. The control and manipulation of Dirac fermions constitute a fundamental step toward the realization of novel concepts of electronic devices and quantum computation. By means of Angle-Resolved Photo-Emission Spectroscopy (ARPES) experiments and ab initio simulations, here, we show that Dirac states can be effectively tuned by doping a transition metal sulfide, BaNiS2, through Co/Ni substitution. The symmetry and chemical characteristics of this material, combined with the modification of the charge-transfer gap of BaCo1−xNixS2 across its phase diagram, lead to the formation of Dirac lines, whose position in k-space can be displaced along the Γ−M symmetry direction and their form reshaped. Not only does the doping x tailor the location and shape of the Dirac bands, but it also controls the metal-insulator transition in the same compound, making BaCo1−xNixS2 a model system to functionalize Dirac materials by varying the strength of electron correlations.