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Highly one-dimensional (1D) Fermi sheets are realized at the surface of a layered Ir telluride IrTe2 which exhibits a stripe-type charge and orbital order below ∼280 K. The 1D Fermi sheets appear in the low temperature range where the stripe order is well established. The 1D Fermi sheets are truncated by the bulk Fermi surfaces, and the spectral weight suppression at the Fermi level deviates from the typical Tomonaga–Luttinger behavior. The 1D band runs along the stripe and is accompanied by several branches which can be derived from the quantization in the perpendicular direction.

We have studied the multi-band electronic structure of ferromagnetic CeRuPO (TC = 15 K) by means of angle-resolved photoemission spectroscopy (ARPES). The ARPES results show that three hole bands exist around the zone center and two of them cross the Fermi level (EF). Around the zone corner, two electron bands are observed and cross EF. These hole and electron bands, which can be assigned to the Ru 4d bands, are basically consistent with the band-structure calculation including their orbital characters. However, one of the electron bands with Ru 4d 3z2 − r2 character is strongly renormalized indicating correlation effect due to hybridization with the Ce 4f orbitals. The Ru 4d 3z2 − r2 band changes across TC suggesting that the out-of-plane 3z2 − r2 orbital channel plays essential roles in the ferromagnetism.

We investigate the temperature-induced mixed valence transition in EuNi 2 (Si 0.20 Ge 0.80 ) 2 using Hard X-ray (5940 eV) photoemission spectroscopy (HX-PES), with a probing depth larger than 5 nm....

We have studied the substitution and temperature dependences of the B s p -Yb d -derived conduction-band states in Yb 1- x Lu x B 12 ( x = 0.25, 0.50, 0.75, and 1.00) by high-resolution photoemissi...

Using polarized oxygen K edge spectroscopy, the first unoccupied orbital of LaSrMnO 4 was investigated. The lowest unoccupied orbital is of minority spin d x z , d y z character instead of the majority spin d x 2 - y 2 character. The d x 2 - y 2 orbital would be expected based on Hund's rule and the strong exchange interaction of the one-electron addition d 5 system. The explanation is a strong ligand field splitting caused by the strong local site distortion of the Mn site which raises the energy of the majority spin d x 2 - y 2 orbital and lowers the energy of the d x z , d y z orbitals. At the same time the two-electron integrals, which are responsible for the exchange interaction, are screened because of covalency.

Resonant photoemission experiments in the Mn 2 p -3 d excitation region of NiAs-type MnTe have been performed. The Mn 3 d , 3 p and 3 s photoemission intensities have shown remarkable resonant enha...

Clear changes of the Yb 4f photoemission spectra with temperature are observed in Yb 4 As 3 by high resolution photoemission spectroscopy. The photoemission intensity is very low at the Fermi level and decreases as the temperature is lowered in accord with the narrowing of the 4f spectra. Bulk and surface contributions are deconvoluted in the 4f 13 final state spectra. In comparison with the corresponding results in Yb 4 (As 1- x Sb x ) 3 , the spectral changes of Yb 4 As 3 with temperature are confirmed to be beyond simple thermal broadening effects and related to the charge ordering effects. Although the change from the charge ordering temperature ( T t ) down to about T t /2 is consistent with a theoretical prediction, the change below it is rather unusual and may be ascribed to the incompleteness of the charge ordering effect. Spectral changes with Yb 4 Sb 3 -substitution are qualitatively discussed.

We have investigated the magnetic behaviors of molecularly thin Mn-doped titanium oxide nanosheets by X-ray magnetic circular dichroism. Mn atoms in single-layer nanosheets showed a weak ferromagnetic order at room temperature. Fe overlayers deposited on the nanosheets induced a magnetic proximity effect on Mn magnetization. We clearly observed an antiferromagnetic coupling between the Fe overlayers and the Mn-doped nanosheets.

Ultraviolet photoemission spectra have been measured for Ce 2 Sb, CeBi 0.9 Te 0.1 and CeSe by use of synchrotron radiation to study their electronic structures especially to study the origin of the double peak structures. We have observed the same double peak structure in CeBi 0.9 Te 0.1 as in CeBi. A remarkable triple peak structure is observed in CeSe attributed to the p , f and d bands respectively. Ce 2 Sb is more complicated but it was shown that the band structure is rather similar to CeSb except for a pseudo-gap between the p and d bands and that the f level is at the pseudo-gap causing no double peak structure.

Two peculiar types of electronic dispersive structures, irreproducible in bulk band calculations, have been observed in quasi-one-dimensional TlSe studied by angle-resolved photoemission spectroscopy. One is of the cross type centered at the Γ point and extending along the Γ–H–T direction parallel to the chains, which are formed along the crystallographic c-axis. The other is of the pyramid type with truncated pyramids regularly arranged along the Γ–N direction perpendicular to the chains. To an extent given by the obtained excitation photon energy dependence, the above electronic structures can be assigned to high-lying surface conduction bands resulting from secondary electron emission.

The electronic band structure of ordered FePt 3 (110) single crystal was studied by angle-resolved photoemission spectroscopy with synchrotron radiation. The energy band dispersions along the X –Γ– X and R – M – R directions of a simple cubic Brillouin zone were successfully observed at room temperature. Along the latter direction, band folding due to antiferromagnetic (AF) ordering was clearly observed below the Neel temperature ( T N2 ) of 100 K. Through comparison with theoretical calculations, (1/2, 0, 0)-type AF ordering or a mixture of the (1/2, 0, 0)-type and (1/2, 1/2, 0)-type AF orderings was concluded to occur below T N2 . These magnetic orderings can be understood from the viewpoint of the nesting between the electron and hole pockets.

We have performed photoemission spectroscopy studies of single-crystalline CuV 2 S 4 using synchrotron radiation, in order to clarify the electronic structure changes across the charge density wave (CDW) transitions in a spinel type compound. Photo-energy-dependent studies show a peak structure just below the Fermi level ( E F ), which undergoes resonant enhancement at an excitation energy h ν= 54.5 eV. This energy corresponds to the V 3 p –3 d threshold energy, thus suggesting that the density of states (DOS) at E F is mainly composed of V 3 d states. From temperature-dependent measurements, we observe a reduction in spectral DOS at and near E F , leading to the formation of a pseudogap across CDW transition temperatures. The pseudogap energy scale of ∼0.05 eV, identified at the top of the valence band, is significantly larger than the value expected from a BCS-like transition.

We have performed the O 1 s x-ray absorption (XAS) and resonant inverse photoemission spectroscopy (RIPES) in Mott insulator YTiO 3 , band insulator CaTiO 3 and Y 0.61 Ca 0.39 TiO 3 with a metal–in...

The Ti 3 d electronic structure of Ti 2 O 3 across metal–insulator transition (MIT) has been investigated by means of polarization-dependent soft X-ray absorption spectroscopy (XAS) at the Ti 2 p edge. The XAS spectra exhibit a remarkable linear dichroism (LD) between the polarization vectors of the incident light parallel and perpendicular to the Ti ion pair along the c -axis. LD intensity is significantly reduced at 520 K in the metallic phase in comparison with that at 300 K in the insulating phase, indicating a large change in a 1 g and e g π orbital occupations. The results are qualitatively consistent with a recent theory, where the MIT is due to the change of the 3 d electronic configuration in the Ti pair along the c -axis driven by a change in the t 2 g level splitting relative to the on-site exchange interaction.

X-ray and vacuum ultraviolet photoemission spectra were measured for valence fluctuating Yb 4 X 3 (X: As, Sb and Bi) by use of Mg K α and synchrotron radiation source. From the line shape analysis of the Yb 4 f spectra, the mean valence is evaluated as 2.32, 2.34 and 2.10 for Yb 4 As 3 ,Yb 4 Sb 3 and Yb 4 Bi 3 . The surface Yb 4 f level shift is estimated as 0.65, 0.63 and 0.59 eV, respectively. The plasmon satellite is confirmed in the Yb 4 f and Yb 4 d core XPS spectra of Yb 4 Bi 3 in contrast to those in Yb 4 As 3 and YbAs. As for the anionic states, the Bi 5 d core UPS spectrum showed a remarkable asymmetry in contrast to the rather symmetric Bi 4 f core XPS spectrum. This result suggests a contribution of the surface Bi 5 d state at larger binding energies of about 0.5 eV.

Far-infrared absorption spectra in As- or Sb-doped germanium in the intermediate impurity concentration range have been investigated at 1.5 K. A steep rising of the absorption toward higher energies is found in the spectra, and their energies are closely connected with the thermal activation energies e 2 's which are determined by simultaneous measurements of the D.C. resistivity. The concentration effect and [111]-uniaxial compressive stress effect have shown that the absorption is attributed to the electronic transition from the impurity ground states to the upper Hubbard band. The evidence of the variable-range hopping is obtained from the shape of the tail of the spectra.

Photoemission experiment was carried out on a (100) surface of Fe 3 O 4 at room temperature, for the incident photon energies between 30.5 and 140 eV, and the results were compared with the band structure calculated by APW method (J. Phys. Soc. Jpn. 53 (1984) 312). Peaks due to the Fe(3 d )–O(2 p ) valence band, O(2 s ) band, Fe(3 p ) band and Auger electrons were observed. Valence band emission starts from the Fermi level indicating that Fe 3 O 4 is a “metal”, not an “insulator with electron diffusion”. Several peaks are distinguished in angle-resolved normal emission spectra in the valence band region. Other peaks are broad and do not show any structure. As a whole, applicability of the calculated band structure is proved. Resonant enhancement of photoemission is observed near the Fe(3 p ) core excitation region. Two subsidiary peaks at 7.5 and 11 eV are tentatively assigned to satellites due to a singlet and a triplet hole pair, respectively. Correlation energy between 3 d electrons is estimated from t...

Absorption spectra resulting from the inner 3p-shell excitation of transition metal ions in halide compounds are measured in the photon energy range from 25 to 140 eV with synchrotron radiation from SOR-RING. The observed characteristic multiplet structures spreading over 10–20 eV are well explained by the localized excitation model for the 3p 5 3d m+1 excited states, providing the evaluation of the final state interactions. The asymmetry of the absorption bands of the transition metal compounds with more than half-filled 3d-shell is interpreted as due to the interference caused by the super Coster-Kronig transition, in contrast to the rather symmetric and broad spectral line shape in the compounds with less than half-filled 3d-shell.

Isolated D - states in Sb-and As-doped germanium crystals have been studied by means of long-wavelength (submillimeter plus millimeter) photoconductivity measurements with a lamellar grating Fourier transform spectrometer at an extremely low temperature, 0.38 K. The electron binding energies of the isolated D - states are accurately determined and the shift of the D - state energy is clearly observed between the samples with different impurities. The many valley effect of the conduction band on the D - state energy is confirmed by comparing the spectra under high [111] stress with those of stress free. The energy shemes of the D - states in Sb-and As-doped germanium crystals are clarified.

The electron- and spin-states in isolated D - states in Ge have been studied by means of long-wavelength photoconductivities in magnetic fields at 0.35 K. The difference of the photoconductivity spectral behaviors between Sb and As impurities is ascribed to that of the valley-orbit interactions. From the magnetic field dependence of the photoconductivity spectra of the D - complexes, the donor molecules D 2 are supposed to be formed in the crystal in the first stage of increasing the impurity concentration which cause D 2 - states, and further increases of the concentrations result in more complicated D - complexes in the crystal.

Effect of 3d transition metal intercalation into 1T-CdI 2 type TiS 2 layered crystals, expressed as M x TiS 2 (M=Mn, Fe, Co and Ni), has been studied by synchrotron radiation photoemission over the photon energy range of \(\hbar\omega=32\text{--}120\) eV. The spectra are found to depend strongly on the guest 3d metals and their conacentration. The valence bands are modified by the strong hybridization of Ti 3d, S 3p states and the guest atom 3d states, in good agreement with a theoretical prediction.

Reflectance spectra of FeS 2 , CoS 2 and NiS 2 pyrites have been measured in the photon energy region from 4 to 30 eV with synchrotron radiation and compared with the results of NiO and related compounds. Dielectric constants, optical constants, effective electron numbers as well as energy-loss functions are evaluated by means of the Kramers-Kronig analysis. Fine structures of the reflectance spectra are qualitatively interpreted providing information on band structures. Characteristic features of band structures related to the 3 d electrons in the low-spin state are experimentally elucidated.

Impurity concentration effects on D - states in Sb-doped germanium have been investigated by means of long-wavelength photoconductivity at 0.38 K and 1.46 K. Higher energy shifts of the spectra with increasing the impurity concentration suggest the existence of D - complexes in the samples with Sb-concentrations from 2×10 14 cm -3 to 1×10 16 cm -3 , and [111]-stress effects on the complexes are also studied. A drastic change of the spectral shape at the concentration of 2×10 16 cm -3 in the steps of increasing the concentration is ascribed to the formation of the D - band.

The energy distribution of the 4 f partial density of states in CeCu 6 has been observed by means of the resonant enhancement of the 4 f cross section associated with the excitation of the 4 d electron. The main 4 f line is located 2.3 eV below the Fermi edge. In addition to the main line, states with the 4 f character are distributed all over the valence band. The 3 p -3 d resonances of the Cu 3 d band and its satellite are also found.