Berry curvature unravelled by the Nernst effect in Mn3_3Ge

The discovery of topological quantum materials represents a striking innovation in modern condensed matter physics with remarkable fundamental and technological implications. Their classification has been recently extended to topological Weyl semimetals, i.e., solid state systems which exhibit the elusive Weyl fermions as low-energy excitations. Here we show that the Nernst effect can be exploited as a sensitive probe for determining key parameters of the Weyl physics, applying it to the non-collinear antiferromagnet Mn$_3$Ge. This compound exhibits anomalous thermoelectric transport due to enhanced Berry curvature from Weyl points located extremely close to the Fermi level. We establish from our data a direct measure of the Berry curvature at the Fermi level and, using a minimal model of a Weyl semimetal, extract for the first time the Weyl point energy and their distance in momentum-space

Hydrophilic 1,10-phenanthroline derivatives for selective Am(III) stripping into aqueous solutions

The novel and fully combustible hydrophilic 1,10-phenanthroline-2,9-dicarboxamide (1) was synthesized and investigated as Am(III) stripping agent in a simulated advanced hydrometallurgical process, in comparison with two other 1,10-phenanthroline-based ligands 2 and 3. The stripping efficiency and the Am(III)/lanthanides(III) selectivity of the TODGA (org)/phen-derivative (aq) extracting system were studied under several experimental conditions by liquid–liquid extraction tests. The results obtained clarify the main limitations of these ligands in the scope of the hydrometallurgical reprocessing but also enable to get indications to steer future investigations in the domain of the selective An(III) recovery for the advanced reprocessing of Spent Nuclear Fuel by hydrophilic ligands

Electronic correlations and nematicity in 122 and 1111 Fe-based superconductors

This work gives insight in some key aspects for the understanding of the origin of high-temperature superconductivity in the newly discovered class of iron-based materials. In particular, thermodynamic methods, such as SQUID magnetometry, specific heat and dilatometry were used, in order to (i) assess the evolution of electronic correlations in a series of transition metal substitutions of the well-known BaFe2As2 as a function of 3d band filling and (ii) to re-investigate the phase diagram of Co-doped LaFeAsO on single crystals, with particular interest in the interplay between the nematic/magnetic phase of the parent compound and superconductivity induced by in-plane electron doping. In the first part of this work, the Sommerfeld coefficient (γ_exp) was extracted from the low temperature specific heat data and compared with the theoretical values obtained by band theory calculations, in order to obtain the mass enhancement (m∗/mb) in the series BaT2As2 (T = Cr, Mn, Fe, Co, Ni, Cu). The results clearly show an overall decrease of the electronic correlations while departing from the half-filled (3d5) to the fully filled configuration (3d10), thus suggesting a highly correlated 3d5 state. The evolution of electronic correlations as a function of 3d band filling for n > 5 is in agreement with previous theoretical calculations, underlining the importance of Hund’s coupling in describing the normal-state properties of iron-based superconductors. In addition, it was found that the decrease in m∗/mb for n > 5 follows an increase of the crystal field splitting (Δ), determined by the progressive distortion of the As-T-As angle (α_bond) from the ideal tetrahedral environment. This study reveals a complex interplay between electronic correlations, band filling and crystal structure in determining the physical properties of 122 systems. In the second part, the phase diagram of Co-doped LaFeAsO was re-investigated using single crystals by thermodynamic methods. From magnetic susceptibility studies we track the doping evolution of the antiferromagnetic phase, revealing a continuous decrease of T_N up to 5% Co doping. In order to study the evolution of the so-called nematic phase, the temperature dependence of the length changes along the a and b orthorhombic directions, ΔL/L_0, was determined by high-resolution capacitance dilatometry. The results clearly show a gradual reduction of the orthorhombic distortion δ and of T_S with increasing Co content up to 4.5%, while it is completely suppressed for 7.5% Co. Bulk superconductivity with T_c = 10.5 K was found in a small doping region around 6% Co content, while both T_c and the superconducting volume fraction rapidly drop in the neighbouring doping regime. Ultimately, no microscopic coexistence between the superconducting and magnetic phases can be assessed within our resolution limit, in sharp contrast with other iron-pnictide families, e.g., electron- and hole-doped BaFe2As2

Electronic correlations and nematicity in 122 and 1111 Fe-based superconductors

This work gives insight in some key aspects for the understanding of the origin of high-temperature superconductivity in the newly discovered class of iron-based materials. In particular, thermodynamic methods, such as SQUID magnetometry, specific heat and dilatometry were used, in order to (i) assess the evolution of electronic correlations in a series of transition metal substitutions of the well-known BaFe2As2 as a function of 3d band filling and (ii) to re-investigate the phase diagram of Co-doped LaFeAsO on single crystals, with particular interest in the interplay between the nematic/magnetic phase of the parent compound and superconductivity induced by in-plane electron doping. In the first part of this work, the Sommerfeld coefficient (γ_exp) was extracted from the low temperature specific heat data and compared with the theoretical values obtained by band theory calculations, in order to obtain the mass enhancement (m∗/mb) in the series BaT2As2 (T = Cr, Mn, Fe, Co, Ni, Cu). The results clearly show an overall decrease of the electronic correlations while departing from the half-filled (3d5) to the fully filled configuration (3d10), thus suggesting a highly correlated 3d5 state. The evolution of electronic correlations as a function of 3d band filling for n > 5 is in agreement with previous theoretical calculations, underlining the importance of Hund’s coupling in describing the normal-state properties of iron-based superconductors. In addition, it was found that the decrease in m∗/mb for n > 5 follows an increase of the crystal field splitting (Δ), determined by the progressive distortion of the As-T-As angle (α_bond) from the ideal tetrahedral environment. This study reveals a complex interplay between electronic correlations, band filling and crystal structure in determining the physical properties of 122 systems. In the second part, the phase diagram of Co-doped LaFeAsO was re-investigated using single crystals by thermodynamic methods. From magnetic susceptibility studies we track the doping evolution of the antiferromagnetic phase, revealing a continuous decrease of T_N up to 5% Co doping. In order to study the evolution of the so-called nematic phase, the temperature dependence of the length changes along the a and b orthorhombic directions, ΔL/L_0, was determined by high-resolution capacitance dilatometry. The results clearly show a gradual reduction of the orthorhombic distortion δ and of T_S with increasing Co content up to 4.5%, while it is completely suppressed for 7.5% Co. Bulk superconductivity with T_c = 10.5 K was found in a small doping region around 6% Co content, while both T_c and the superconducting volume fraction rapidly drop in the neighbouring doping regime. Ultimately, no microscopic coexistence between the superconducting and magnetic phases can be assessed within our resolution limit, in sharp contrast with other iron-pnictide families, e.g., electron- and hole-doped BaFe2As2

Electronic correlations and nematicity in 122 and 1111 Fe-based superconductors

This work gives insight in some key aspects for the understanding of the origin of high-temperature superconductivity in the newly discovered class of iron-based materials. In particular, thermodynamic methods, such as SQUID magnetometry, specific heat and dilatometry were used, in order to (i) assess the evolution of electronic correlations in a series of transition metal substitutions of the well-known BaFe2As2 as a function of 3d band filling and (ii) to re-investigate the phase diagram of Co-doped LaFeAsO on single crystals, with particular interest in the interplay between the nematic/magnetic phase of the parent compound and superconductivity induced by in-plane electron doping. In the first part of this work, the Sommerfeld coefficient (γ_exp) was extracted from the low temperature specific heat data and compared with the theoretical values obtained by band theory calculations, in order to obtain the mass enhancement (m∗/mb) in the series BaT2As2 (T = Cr, Mn, Fe, Co, Ni, Cu). The results clearly show an overall decrease of the electronic correlations while departing from the half-filled (3d5) to the fully filled configuration (3d10), thus suggesting a highly correlated 3d5 state. The evolution of electronic correlations as a function of 3d band filling for n > 5 is in agreement with previous theoretical calculations, underlining the importance of Hund’s coupling in describing the normal-state properties of iron-based superconductors. In addition, it was found that the decrease in m∗/mb for n > 5 follows an increase of the crystal field splitting (Δ), determined by the progressive distortion of the As-T-As angle (α_bond) from the ideal tetrahedral environment. This study reveals a complex interplay between electronic correlations, band filling and crystal structure in determining the physical properties of 122 systems. In the second part, the phase diagram of Co-doped LaFeAsO was re-investigated using single crystals by thermodynamic methods. From magnetic susceptibility studies we track the doping evolution of the antiferromagnetic phase, revealing a continuous decrease of T_N up to 5% Co doping. In order to study the evolution of the so-called nematic phase, the temperature dependence of the length changes along the a and b orthorhombic directions, ΔL/L_0, was determined by high-resolution capacitance dilatometry. The results clearly show a gradual reduction of the orthorhombic distortion δ and of T_S with increasing Co content up to 4.5%, while it is completely suppressed for 7.5% Co. Bulk superconductivity with T_c = 10.5 K was found in a small doping region around 6% Co content, while both T_c and the superconducting volume fraction rapidly drop in the neighbouring doping regime. Ultimately, no microscopic coexistence between the superconducting and magnetic phases can be assessed within our resolution limit, in sharp contrast with other iron-pnictide families, e.g., electron- and hole-doped BaFe2As2

Synthesis of polyaniline-based inks for inkjet printed devices: Electrical characterization highlighting the effect of primary and secondary doping

Engineering applications for printed electronics demand solution processable electrically conductive materials, in the form of inks, to realize interconnections, piezoresistive pressure sensors, thermoresistive temperature sensors, and many other devices. Polyaniline is an intrinsically conductive polymer with modest electrical properties but clear advantages in terms of solubility and stability with temperature and in time. A comprehensive study, starting from its synthesis, primary doping, inkjet printing and secondary doping is presented, with the aim of elucidating the doping agent effects on its morphology, printability and electronic performanc

2,9-Dicarbonyl-1,10-phenanthroline derivatives with an unprecedented Am(iii)/Eu(iii) selectivity under highly acidic conditions

Four lipophilic 1,10-phenanthroline di(thio)amide, diester or diketone derivatives were studied as ligands for Am(III)/Eu(III) separation from acidic media. The synthesis of these compounds is reported together with the extraction tests in different solvents (kerosene, octanol and o-nitrophenyl hexyl ether), HNO3 concentrations and ratios between the ligand and the synergistic agent (Br–Cosan). The promising results obtained from the large number of solvent extraction tests carried out show that it might be possible to apply this class of ligands to advanced reprocessing of spent nuclear fuel. The experimental data indicate that, under the conditions that simulate the real radioactive waste, the extraction efficiency and Am/Eu separation factors are particularly high, thus suggesting that the combination of soft heterocyclic N-donor atoms and hard carbonyl groups of ester and amides affords a tetradentate donor set of atoms (ONNO) that gives rise to remarkable selectivities. ESI-MS studies and DFT calculations shed light on the possible structure of the Eu3+ complexes indicating that the 1 : 1 : 2 (cation : ligand : anion) complex is slightly more stable than the 1 : 2 : 1 species