We examined the zero-field splitting of an iron(II) phthalocyanine (FePc) attached to clean and oxidized Cu(110) surfaces and the dependence on an applied magnetic field by inelastic electron tunneling spectroscopy with STM. The symmetry of the ligand field surrounding the Fe atom is lowered on the oxidized surface, switching the magnetic anisotropy from the easy plane of the bulk to the easy axis. The zero-field splitting was not observed for FePc on a clean Cu(110) surface, and the spin state converts from triplet to singlet due to the strong coupling of Fe d states with the Cu substrate, as is also confirmed by photoelectron spectroscopy. These findings demonstrate the importance of coupling at the molecule-substrate interface for manipulating the magnetic properties of adsorbates.

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High-resolution x-ray photoelectron spectroscopy (XPS) at 6 keV photon energy has been realized utilizing high-flux-density x rays from the third generation high-energy synchrotron radiation facility, SPring-8. The method has been applied to analysis of high-k HfO2/interlayer/Si complementary metal–oxide–semiconductor gate-dielectric structures. With the high energy resolution and high throughput of our system, chemical-state differences were observed in the Si 1s, Hf 3d, and O 1s peaks for as-deposited and annealed samples. The results revealed that a SiOxNy interlayer is more effective in controlling the interface structure than SiO2. Our results show the wide applicability of high resolution XPS with hard x rays from a synchrotron source.

We have reexamined the valence-band (VB) and core-level electronic structure of NiO by means of hard and soft x-ray photoemission spectroscopies. The spectral weight of the lowest energy state was found to be enhanced in the bulk sensitive Ni 2p core-level spectrum. A configuration-interaction model including a bound state screening has shown agreement with the core-level spectrum and off- and on-resonance VB spectra. These results identify the lowest energy states in the core-level and VB spectra as the Zhang-Rice (ZR) doublet bound states, consistent with the spin-fermion model and recent ab initio calculations within dynamical mean-field theory. The results indicate that the ZR character first ionization (the lowest hole-addition) states are responsible for transport properties in NiO and doped NiO.

Using hard x-ray (HX; hν = 5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La1−xSrxMnO3 (LSMO) thin films. Comparison of Mn 2p corelevels with Soft x-ray (SX; hν ∼ 1000 eV) -PES shows a clear additional well-screened feature only in HX-PES. Take-off-angle dependent data indicate its bulk (≥ 20Å) character. The doping and temperature dependence track the ferromagnetism and metallicity of the LSMO series. Cluster model calculations including charge transfer from doping induced states show good agreement, confirming this picture of bulk properties reflected in Mn 2p core-levels using HX-PES.PACS numbers: 71.30.+h, 78.20.Bh Hole-doped manganese oxides with a perovskite structure of Re 1−x Ae x MnO 3 (Re and Ae being trivalent rare earth : Nd, Pr, Sm, etc. and divalent alkaline earth elements : Ca, Sr, Ba, respectively) exhibit a rich phase diagram originating in complex collective phenomena due to interplay among spin, charge, orbital, and lattice degrees of freedom [1,2]. Among the manganites, La 1−x Sr x MnO 3 (LSMO) is a prototypical series showing the largest one-electron bandwidth and accordingly, is less significantly affected by electron-lattice and Coulomb correlation effects [2]. The parent compound LaMnO 3 is an antiferromagnetic (AFM) insulator which becomes, on hole-doping induced by substitution of Sr for La, a ferromagnetic (FM) metal [3] exhibiting colossal magnetoresistance (CMR). The optimal doped compound (x = 0.4) exhibits the highest Curie temperature (T C ) of 360 K among manganites and a half-metallic nature [4]. Further hole-doping induces a magnetic transition, transforming the FM metal to an AFM metal phase for x > 0.5 [5]. In the case of thin films, the critical temperature and resistivity change slightly compared to the bulk materials due to the strain from the substrate, but the qualitative physical properties are similar to the bulk materials, provided the films are at least ∼ 10 unit cells (∼ 30Å) thick [6,7,8,9].In particular, high-quality bulk and thin films of the LSMO series do not exhibit charge order and are also free of micro-and nano-scale phase separation phenomena seen in the La-Ca, Nd-Sr and Pr-Sr manganites [2]. However, ultra thin films of LSMO (i.e. < 30Å or 10 unit cell thickness) are known to show a suppression of metallicity, ferromagnetic T C and magnetization [6,7]. In order to clarify the origin of these unusual physical properties, it is important to investigate the electronic structure of LSMO with a depth sensitive probe. Photoemission spectroscopy (PES) has long played a central role in studying the electronic structure of strongly correlated electron systems including manganese oxides [9,10,11,12,13,14]. Temperature dependent half-metallic ferromagnetism, charge and orbital ordering, and its connection with the electronic structure and colossal magnetoresistance of the manganites have been clarified [11,12,13]. Nevertheless, the change in the Mn 2p spectra of manganese oxides with hole doping is still not...

Electronic structures of the quantum critical superconductor β-YbAlB4 and its polymorph α-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb 3d core level spectra, the values of the Yb valence are estimated to be ∼2.73 and ∼2.75 for α- and β-YbAlB4, respectively, thus providing clear evidence for valence fluctuations. The valence band spectra of these compounds also show Yb2+ peaks at the Fermi level. These observations establish an unambiguous case of a strong mixed valence at quantum criticality for the first time among heavy fermion systems, calling for a novel scheme for a quantum critical model beyond the conventional Doniach picture in β-YbAlB4.

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.

The temperature ͑T͒-dependent metal-insulator transition ͑MIT͒ in VO 2 is investigated using bulk sensitive hard-x-ray ͑ϳ8 keV͒ valence-band, core-level, and V 2p −3d resonant photoemission spectroscopies ͑PESs͒. The valence-band and core-level spectra are compared with full-multiplet cluster model calculations including a coherent screening channel. Across the MIT, V 3d spectral weight transfer from the coherent ͑3d 1 C គ final͒ states at Fermi level to the incoherent ͑3d 0 +3d 1 L គ final͒ states, corresponding to the lower Hubbard band, leads to gap formation. The spectral shape changes in V 1s and V 2p core levels as well as the valence band are nicely reproduced from cluster model calculations, providing electronic structure parameters. Resonant PES finds that the 3d 1 L គ states resonate across the V 2p −3d threshold in addition to the 3d 0 and 3d 1 C គ states. The results support a Mott-Hubbard transition picture for the first-order MIT in VO 2 .