S. R. Krishnakumar

Electronic structure of Millerite NiS

We investigate the electronic structure of Nickel sulphide (NiS) in the millerite phase using electron spectroscopic measurements and band structure as well as model Hamiltonian calculations. While band structure calculations are found to be relatively more successful in describing the experimental valence band spectrum of this highly conducting phase compared to the hexagonal phase of NiS, cluster calculations including electron correlation effects are found to be necessary for the description of certain features in the experimental spectra, indicating the importance of correlation effects even in a highly metallic system. The electronic parameter strengths obtained from these calculations confirm that the millerite NiS is a highly covalent pd metal. The comparative study of hexagonal and millerite forms of NiS, provides the information concerning the evolution of the spectral function in a pd metal as a function of covalency.

X-ray photoemission study of NiS 2 − x Se x ( x = 0.0 – 1 . 2 )

Electronic structure of NiS_{2-x}Se_x system has been investigated for various compositions (x) using x-ray photoemission spectroscopy. An analysis of the core level as well as the valence band spectra of NiS_2 in conjunction with many-body cluster calculations provides a quantitative description of the electronic structure of this compound. With increasing Se content, the on-site Coulomb correlation strength (U) does not change, while the band width W of the system increases, driving the system from a covalent insulating state to a pd-metallic state.

Electronic structure of NiS 1 − x Se x

We investigate the electronic structure of the metallic

TEMPERATURE-DEPENDENT PHOTOEMISSION SPECTRAL WEIGHT IN LA0.6SR0.4MNO3

NiS_{1-x}Se_x

Electronic structure of NiS1 xSex across the phase transition

system using various electron spectroscopic techniques. The band-structure results do not describe the details of the spectral features in the experimental spectrum, even for this paramagnetic metallic phase. However, a parametrized many-body multiband model is found to be successful in describing the Ni 2p core level and valence band, within the same model. The asymmetric line shape as well as the weak intensity feature in the Ni 2p core-level spectrum have been ascribed to extrinsic loss processes in the system. The presence of satellite features in the valence-band spectrum shows the existence of the lower Hubbard band, deep inside the pd metallic regime, consistent with the predictions of the dynamical mean-field theory.