The structural and electronic properties of the skutterudite-related Ce${}_{3}$$M$${}_{4}$Sn${}_{13}$ and La${}_{3}$$M$${}_{4}$Sn${}_{13}$ intermetallic compounds with $M=\text{Co}$, Ru, and Rh have been investigated. A subtle structural transition from a simple cubic phase (Yb${}_{3}$Rh${}_{4}$Sn${}_{13}$-type structure) to the superlattice variant at ${T}_{D}$\sim${}160$ K has been evidenced by x-ray diffraction, resistivity, and specific-heat data. Recently, a high charge density between metal $M$ and Sn atoms was calculated for Ce${}_{3}$Rh${}_{4}$Sn${}_{13}$ and Ce${}_{3}$Co${}_{4}$Sn${}_{13}$. The strong charge accumulation implies a strong $M$-Sn2 covalent bonding interaction. In consequence, a local distortion of the trigonal Sn prisms around metal $M$ can modify the electronic structure of the system. The main goal of this report is to study the electronic structure in the family of RE${}_{3}$$M$${}_{4}$Sn${}_{13}$, where $\text{RE}=\text{Ce}$ or La above and below ${T}_{D}$. We show that the Sn $4d$ x-ray photoelectron spectroscopy spectra have the complex structure, which can be interpreted as a result of different charge distribution around Sn atoms. The shape of the $4d$ Sn lines is also temperature dependent, which we attribute to the local distortion of the Sn2 cages in RE${}_{3}$$M$${}_{4}$Sn${}_{13}$.

We present an investigation of the magnetic, thermodynamic, and electric transport properties and the electronic structure of the strongly correlated compounds Ce${}_{3}$Rh${}_{4}$Sn${}_{13}$ and Ce${}_{3}$Co${}_{4}$Sn${}_{13}$. The main goal of this report is to compare the physical properties of both compounds and to explain the abnormal electrical resistivity behavior in Ce${}_{3}$Co${}_{4}$Sn${}_{13}$ above $$\sim${}160$ K, which has not been observed in Ce${}_{3}$Rh${}_{4}$Sn${}_{13}$. We suggest that a possible local distortion of the trigonal Sn2 prisms around Co occurs in Ce${}_{3}$Co${}_{4}$Sn${}_{13}$ below $$\sim${}160$ K, which could change the electronic structure near the Fermi level and, as a consequence, explain the metallic behavior visible in the resistivity above this temperature. We determined experimentally the hybridization energy $$\Delta${}$ between the $f$-electron and conduction-electron states for both compounds and its influence on the different $$\rho${}(T)$ behaviors under pressure. The complimentary experimental data allowed us to explain the semimetallic properties of both compounds and the transition between semimetallic and metallic behavior in Ce${}_{3}$Co${}_{4}$Sn${}_{13}$, which is not observed for Ce${}_{3}$Rh${}_{4}$Sn${}_{13}$.

We discuss and interpret the properties of the $\mathrm{Ce}\mathrm{Rh}{\mathrm{Sb}}_{1-x}{\mathrm{Sn}}_x$ systems in the concentration interval $0⩽x<0.2$. For $x\cong 0.13$ a quantum critical point has been observed by us recently and separates the Kondo-insulator (KI) from the metallic non-Fermi-liquid (NFL) state. We present the temperature dependence of the resistivity, the ac and dc magnetic susceptibilities, the specific heat, and the magnetization data through the critical concentration regime $x\sim 0.12–0.13$, as well as provide their discussion in terms of the transition from the nonmagnetic (Kondo-lattice) insulator to a weakly magnetic and singular non-Fermi liquid. The difference between the Kondo-lattice and the Mott-Hubbard semiconductors at temperature $T>0$ is emphasized. Also, the difference between those two types of insulating states is discussed. On the basis of the experimental results we propose a schematic phase diagram on the plane $T\text{−}x$ and demonstrate the rationale for the existence of the quantum critical point separating KI and NFL phases. Namely, we propose that the metallization of the insulating Kondo lattice in terms of the collective spin-singlet Kondo-lattice state destruction and a concomitant delocalization of the $4f$ electrons, within an effective $f$-band model of correlated electrons undergoing the phase transition to the insulating state.

We investigate the electronic structure of the skutterudite-related ${\mathrm{Ce}}_3{M}_4{\mathrm{Sn}}_{13}$ compounds, where metal $M$ is Co, Ru, or Rh, using x-ray photoemission spectroscopy (XPS) and band structure calculations, both within local density approximation scheme and within scheme including additional Coulomb correlations (LDA+$U$). The $d$-electron states located near the Fermi level slightly change the intensity with applying the correlation energy $U$. We note the large impact of $d$-electron correlation, which is clearly observed in the change of Ce $5p$ states located about 18 eV in the valence band. Namely, for ${\mathrm{Ce}}_3{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ and ${\mathrm{Ce}}_3{\mathrm{Ru}}_4{\mathrm{Sn}}_{13}$ the $d$-electron correlations significantly shift the $5p$ states towards higher binding energies, while for ${\mathrm{Ce}}_3{\mathrm{Co}}_4{\mathrm{Sn}}_{13}$ the energy of the Ce $5p$ states almost does not depend on $U$. The influence of the $d$-electron correlations is also manifested by the positive magnetoresistivity (MR) of ${\mathrm{Ce}}_3{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ and the ${\mathrm{Ce}}_{3-x}{\mathrm{La}}_x{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ alloys that reaches 40% at the highest magnetic field ($B=9$ T) for the sample $x=0.6$, whereas only a small positive $\text{MR}\sim 0.5\%$ is observed in ${\mathrm{Ce}}_3{\mathrm{Ru}}_4{\mathrm{Sn}}_{13}$. The magnetoresistivity of ${\mathrm{Ce}}_3{\mathrm{Co}}_4{\mathrm{Sn}}_{13}$ exhibits quite different behavior and is negative.

The aim of this work is to investigate electronic structure, magnetic susceptibility, specific heat, and electrical resistivity of ${\text{Fe}}_2\text{VGa}$ and the series of ${\text{Fe}}_2{\text{V}}_{1-x}{\text{Ti}}_x\text{Ga}$ Heusler alloys. We report x-ray photoelectron valence-band spectra and compare the results with those obtained from full potential linear augmented plane wave method. ${\text{Fe}}_2\text{VGa}$ is calculated as nonmagnetic semimetal with a pseudogap located at the Fermi level. Disordered Fe atoms which occupy the V sites, make magnetic clusters, which give rise to negative giant magnetoresistance (GMR). We found that the Kondo coupling between the low density of carrier and the magnetic moments is not sufficient to screen the moments, which form a superparamagnetic state below $\sim 20\text{K}$. The low temperature decrease in the resistivity and the GMR effect result from a decreased magnetic scattering as the compound orders magnetically. A detailed analysis of the transport and thermodynamic properties reveal a metal-insulator transition in ${\text{Fe}}_2\text{VGa}$, closely resembling that of Mn doped FeSi. The Ti doping increases the density of carriers, in consequence the system for $x>0.2$ is metallic.

The magnetic and transport properties of Fe2VGa doped with metal M (M = Rh and Ti) have been obtained from the analysis of ac magnetic susceptibility $\chi${}ac, magnetization M vs magnetic field, specific heat C, and electrical resistivity $\rho${}. The results provide evidence for the formation of a spin-glass state at Tf$\sim${}6 K, resulting from an atomic disorder. Short-range magnetic correlations manifested at T>Tf as anomalies of the low magnetic field ac magnetic susceptibility and specific-heat data are believed to be related to a Griffiths-like phase in Fe2V1$-${}xMxGa at x<xc$\sim${}0.15.