H. Kumigashira

High-resolution angle-resolved photoemission study of UN and USb; Dual character of 5f electrons

Abstract We have performed high-resolution angle-resolved photoemission spectroscopy on UN and USb to study the electronic structure near the Fermi level ( E F ) and the nature of U 5f electrons. We found that the pnictogen (N and Sb) p bands are fully occupied in contrast with Ce monopnictides and shows a good qualitative agreement with the band calculation by treating the U 5f states as bands. On the other hand, we have not observed dispersive U 5f bands near E F predicted by the band calculation, instead we found two non-dispersive bands near E F , which are assigned as the 5f 2 -final-state multiplet indicative of localized U 5f states. The intensity of multiplet structure is stronger in USb than in UN. These results indicate the dual character of U 5f electrons and its difference between USb and UN.

High-resolution photoemission study of UNi2Al3 and URu2Si2

Abstract High-resolution low-temperature photoemission spectroscopy was performed for UNi 2 Al 3 and URu 2 Si 2 to study the nature of 5 f electrons in U-based heavy fermion materials. Photoemission spectra of both compounds have a sharp peak at E f and a large broad peak around 2 eV, while only UNi 2 Al 3 exhibits an additional small broad feature at 0.6 eV. The two features in the vicinity of E f (the E f -peak and the small structure at 0.6 eV) were found to have a dominant U 5 f character. Comparison with the band structure calculations and experimental results on UPd 2 Al 3 suggests that the E f -peak is ascribed to itinerant U 5 f electrons while the following broad feature at 0.6 eV represents localized f electrons.

Electronic band structure and Fermi surface of URu2Si2 studied by high-resolution angle-resolved photoemission spectroscopy

Abstract We have studied the electronic band structure and the Fermi surface of paramagnetic URu 2 Si 2 with high-resolution angle-resolved photoemission spectroscopy. It was found that Ru 4d bands form a main body of the valence band and exhibit a remarkable energy dispersion in qualitatively good agreement with the band structure calculation. In addition to the dispersive Ru 4d bands, we found a less dispersive band near the Fermi level, which is assigned to the U 5f-Ru 4d hybridized band forming a hole-like Fermi surface at Z point in the Brillouin zone.

Ultrahigh-resolution angle-resolved photoemission spectroscopy of UPd3

Abstract We have studied the electronic band structure and the Fermi surface of UPd 3 with ultrahigh-resolution angle-resolved photoemission spectroscopy. It was found that non-dispersive U 5f “bands” are located far below the Fermi level and the main body of valence band consists of Pd 4d-U 6d hybridized dispersive bands in qualitatively good agreement with the band-structure calculation based on the localized U 5f model. We found two hole-like Fermi surfaces with a dominant Pd 4d character at Γ ( A ) point and an electron-like one with a U 6d nature at K( H ) point.

Electronic structure and Fermi surface of UC studied by high-resolution angle-resolved photoemission spectroscopy

Abstract We have performed high-resolution angle-resolved photoemission spectroscopy on UC to study the band structure and Fermi surface. The valence band structure away from the Fermi level ( E F ) consisting mainly of the C 2p states shows a qualitatively good agreement with the band calculation, suggesting a negligible correlation effect in the C 2p states. In contrast, we found a remarkable narrowing of bands near E F around W point in the Brillouin zone, where a substantial contribution of U 5f states is predicted from the calculation. This suggests the importance of taking into account the correlation effect of U 5f electrons for understanding the electronic structure and physical properties of UC.

4d Core-level resonant photoemission spectroscopy of thulium monochalcogenides around the Tm3d threshold

Abstract We report the results of 4d core-level photoemission spectra for thulium monochalcogenides, TmX (X = S, Se, Te) around the3 d –4 f absorption edge. The resonance effect for Tm4 d emission occurs through partial decay channels of the3 d –4 f excited states. The lifetime-broadening phenomenon, which depends strongly on the binding energy, is also employed here for elucidation of4 d photoelectron spectral features. The behavior of a particular decay channel, referred to as3 d –4 d 4 f , followed by preferential excited states was studied extensively.

Resonant photoemission studies of thulium monochalcogenides around the Tm3d threshold

Abstract We have studied4 f photoemission spectra of thulium monochalcogenides at excitation photon energies of the3 d –4 f resonance region ( hv = 1450–1520 eV). The experimental results are compared with theoretical calculations. The contributions from the4 f divalent part and the trivalent part in the3 d –4 f resonance are more clearly distinguished and resolved than for the4 d -4 f resonant photoemission. The calculated results are in good agreement with the experimental ones both for divalent and trivalent features of thulium ions. We have estimated the mean valence of TmS, TmSe and TmTe samples from3 d absorption spectra and from off-resonant photoemission spectra. The latter should reflect more bulk-sensitive information than that reported for the4 d -4 f resonance region. It is concluded that the3 d –4 f resonant photoemission is a more useful technique to investigate4 f electronic structures than the4 d -4 f photoemission. When we perform the experiments with relatively higher energy resolution.

Hybridization gap in Kondo insulators CeRhSb and CeRhAs studied by ultrahigh-resolution photoemission spectroscopy

Abstract Ultrahigh-resolution photoemission spectroscopy ( Δ E∼8 meV ) has been performed on Kondo insulators CeRhAs and CeRhSb. We found that the 4f-derived density of states shows a depletion (pseudogap) at EF in contrast to metallic Kondo materials. It was also found that the size of both 4f-derived and conduction-electron derived pseudogaps scales well with the Kondo temperature.

Angle-resolved photoemission study of quasi one-dimensional conductor Nb3Te4

Abstract We have performed angle-resolved photoemission spectroscopy on Nb 3 Te 4 , which has zigzag Nb–Nb chains along the c -axis in the crystal. We found a dispersive Nb 4 d band near the Fermi level ( E F ) which crosses E F midway between the center and the boundary of the Brillouin zone in the chain direction. The intensity of the Nb 4 d band was found to be substantially suppressed near/at E F , showing a typical Tomonaga–Luttinger liquid behavior of 1D metals. On the other hand, a clear Fermi-edge cutoff, characteristic of 2D or 3D metals, is seen for this Nb 4 d band. All these results suggest that Nb 3 Te 4 is a quasi 1D metal with admixture of 2D or 3D character due to the finite inter-chain interaction.

High-resolution angle-resolved photoemission study of RSb (R=La, Ce, U)

Abstract High-resolution angle-resolved photoemission spectroscopy has been performed on isostructural RSbs (R=La, Ce, U) to study the electronic band structure near the Fermi level as well as the Fermi-surface topology. We found that USb has a metallic band structure in contrast with semimetallic LaSb and CeSb.