Angle-resolved photoemission study of USb2 the 5f band struc(6)

Single crystal antiferromagnetic USb2 was studied at 15K by angle-resolved photoemission with an overall energy resolution of 24 meV. The measurements unambiguously show the dispersion of extremely narrow bands situated near the Fermi level. The peak at th

Spectra taken at each photon energy were normalized to the intensity above the Fermi edge arising from higher order secondaries. The [001] surfaces were oriented by use of a Laue X-ray camera. The electron energy analyzer was varied between θ = 00 and θ = 6-100, which corresponds to the Γ-X direction in the Brillouin zone.

In the photon energy range of 34-60 eV the photoionization cross-section of U5f increases dramatically with hν and for 60 eV is about twice as high as for 34 eV [23]. In turn, the U6d and the Sb5p (the only shells with cross-sections comparable to the U5f) cross-sections show the opposite photon energy dependence and for hν = 60 eV is approximately three times lower than for hν = 34 eV. The main feature of all of the spectra presented in Fig. 2a, 3 and 4 is the sharp but dispersive peak near the Fermi edge (see Fig. 2b). The structure labeled B situated between 300 meV and 600 meV appears to grow with increasing photon energy up to 60 eV in normal emission PES spectra (Fig.4), unlike the structure at the Fermi edge (A). Using cross-sections argument we relate the feature B mainly to the U5f emission. However, because the structure B is broader than normally ascribed to 5f peaks, we propose that it has a mixed conduction band-5f origin.

By comparison to similar materials containing Sb and f electrons, we do not expect any substantial admixture of the Sb5p state near the Fermi edge. Currently there are no theoretical calculations of the USb2 electronic structure, so we base our assumption on the theoretical and experimental results of USb, CeSb and CeSb2 [24-26]. The comparison of theoretical calculations and photoemission data on USb shows that the U5f state has itinerant rather than localized character. In the itinerant model the Sb5p bands are totally occupied, dispersive, and located 1-4 eV below the Fermi level. There is only a small overlap between the Sb5p and U6d bands. This overlap has little influence on the electronic structure of USb near the Fermi level. We assume similar characteristics for USb2. Although the crystal structure is different, in USb2 the occupied U5f state is also close to the Fermi level and consequently located above the Sb5p band. The interaction between the U5f and the Sb5p electrons results in pushing the Sb5p state towards the higher binding energy [25]. Therefore we would expect that within 0-1 eV

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