Kondo systems are usually described by the interaction of the correlation induced local moments with the highly itinerant conduction electrons. Here, we study the role of electron correlations among conduction electrons in the electronic structure of a Kondo lattice compound, Ce₂CoSi₃, using high resolution photoemission spectroscopy and ab initio band structure calculations, where Co 3d electrons contribute in the conduction band. High energy resolution employed in the measurements helped to reveal the signatures of Ce 4f states derived Kondo resonance features at the Fermi level and the dominance of Co 3d contributions at higher binding energies in the conduction band. The lineshape of the experimental Co 3d band is found to be significantly different from that obtained from the band structure calculations within the local density approximations, LDA. Consideration of electron-electron Coulomb repulsion, U, among Co 3d electrons within the LDA + U method leads to a better representation of experimental results. The signature of an electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. These results clearly demonstrate the importance of the electron correlation among conduction electrons in deriving the microscopic description of such Kondo systems.

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Room temperature Mn K-edge extended X-ray absorption fine structure (EXAFS) studies were carried out on La 1-x Sr x MnO 3+δ (x = 0.1 -0.9) compounds. It is found from the detailed EXAFS analysis that the local structure around Mn sites is different from the global structure inferred from X-ray diffraction, especially for x ≤ 0.4, indicating presence of local distortions in MnO 6 octahedra. For the rhombohedral compounds, x = 0.1 to 0.3 the distortion is maximum for x = 0.1 and two bond lengths are seen-short one in basal plane and long one in apical plane. For compounds with x = 0.4 to 0.8 two short bonds in basal plane and four long bonds-two in the basal plane and remaining two in the apical plane are seen. For the compounds up to x = 0.3 compositions long bond length decreases and short bond length increases with increase in x whereas for the compounds 0.4 ≤ x ≤ 0.8 both types of bond lengths decrease. Such behaviour of bond lengths is an indication of the changed nature of distortion from Jahn-Teller type to breathing type at x = 0.4 composition.

We investigate the electronic structure of CaFe 2 As 2 using high resolution photoemission spectroscopy. Experimental results exhibit three energy bands crossing the Fermi level making hole pockets around the Γ-point. Temperature variation reveal a gradual shift of an energy band away from the Fermi level with the decrease in temperature in addition to the spin density wave (SDW) transition induced Fermi surface reconstruction of the second energy band across SDW transition temperature. The hole pocket in the former case eventually disappears at lower temperatures while the hole Fermi surface of the third energy band possessing finite p orbital character survives till the lowest temperature studied. These results reveal signature of a complex charge redistribution among various energy bands as a function of temperature that might be associated to the exotic properties of this system.

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