We investigate the electronic structure of chromium nitride (CrN) across the first-order magnetostructural transition at T(N)∼286  K. Resonant photoemission spectroscopy (PES) shows a gap in the 3d partial density of states at the Fermi level and an on-site Coulomb energy U∼4.5  eV, indicating strong electron-electron correlations. Bulk-sensitive high-resolution (6 meV) laser PES reveals a clear Fermi edge indicating an antiferromagnetic metal below T(N). Hard x-ray Cr 2p core-level PES shows T-dependent changes across T(N) which originate from screening due to coherent states as substantiated by cluster model calculations using the experimentally observed U. Electrical resistivity confirms an insulator above T(N) (E(g)∼70  meV) becoming a disordered metal below T(N). Thus, CrN transforms from a correlated insulator to an antiferromagnetic metal, coupled to the magnetostructural transition.

Copper single crystals with deformation axes in [001], [112], [111], [212], [101], [102], and [213] supplemented. The stress-strain behaviour and its variation with temperature were observed systematically. The crystal orientations after tensile deformations were determined by the slip lines on the specimen surfaces which were chemically polished after prestrain and extended by a few percent. The results showed that the tensile axes of the [101]

Hard X-ray Photoemission spectroscopy (PES) of copper core electronic states, with a probing depth of ∼60Å, is used to show that the Zhang-Rice singlet feature is present in La2CuO4 but is absent in Nd2CuO4. Hole-and electron doping in La2−xSrxCuO4 (LSCO) and Nd2−xCexCuO4 (NCCO) result in new well-screened features which are missing in soft X-ray PES. Impurity Anderson model calculations establish metallic screening as its origin, which is strongly suppressed within 15Å of the surface. Complemented with X-ray absorption spectroscopy, the small chemical-potential shift in core levels (∼ 0.2 eV) are shown to be consistent with modifications of valence and conduction band states spanning the band gap (∼ 1 eV) upon hole-and electron-doping in LSCO and NCCO. [2]. Soft X-ray (SX, hν∼1000-1500 eV) core level photoemission spectroscopy (PES) with a probing depth of ∼10-15Å is valuable in studying valence change, chemical-potential-shift and screening effects in solids [3]. Combination of core level PES with model calculations have been used to describe the parent insulating cuprates La 2 CuO 4 (LCO) and Nd 2 CuO 4 (NCO) as charge-transfer insulators in the Zaanen-SawatzkyAllen classification scheme [4], with the on-site Coulomb energy (≈8 eV), being much larger than the charge transfer energy (≈2 eV) between the O 2p and Cu 3d states [5,6,7,8].La 1.85 Sr 0.15 CuO 4 (LSCO) and Nd 1.85 Ce 0.15 CuO 4 (NCCO) are prototypical of hole-and electron-doped cuprates and exhibit a d x 2 −y 2 superconducting gap. The normal phase resistivity (ρ∝T 2 ) is like a Fermi-liquid for NCCO[9] but non-Fermi-liquid-like (ρ∝T ) for LSCO [10]. The strong correlations lead to special spectral behaviour such as non-local screening effects [11], and anomalous spectral weight transfer upon doping [12]. While valency and chemical potential changes in the high-Tc cuprates can be probed with SX-PES, in spite of several core level and valence band PES studies, there remains a seemingly simple and yet unresolved puzzle about the doping dependent electronic structure of the superconducting cuprates [5,6,7,8,11,12,13,14,15]. The puzzle involves distinguishing between 'mid-gap pinning' or 'crossing the gap' scenario to simultaneously explain changes in core levels and valence bands. The mid-gap pinning scenario [5,6,14,15] involves formation of new states within the band gap on hole-and electron-doping. It explains the small chemical potential shift of -0.2 eV (or +0.2 eV) in O 1s core levels PES of LSCO (or NCCO) compared to undoped LCO (or NCO), but is inconsistent with the large optical gap onset (∼1.0 eV) of the insulating parents [16]. In an alternative picture, the chemical potential moves to the top of the valence band by hole-doping and bottom of the conduction band on electron-doping. Using resonant PES [13], it was shown that electron-and hole-doping leads to a crossing of the gap (∼1.0 eV) from NCCO to LSCO. However, the small chemical potential shift in O 1s core levels cannot be explained by this scenario.While many SX-PES of the Cu 2p core ...

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