Angle-resolved photoemission study of USb2 the 5f band struc(4)

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

2.Experimental

We present ARPES data of USb2 single crystals taken at low photon energies (20-60 eV) with an overall energy resolution between 24 meV (for hν= 34 eV) and 49 meV (for hν = 60 eV). The USb2 crystals were prepared by the flux growth method and the PES studies were performed at the Synchrotron Radiation Center in Stoughton, Wisconsin.

We used a Plane Grating Monochromator (PGM) and estimate that the shifts of the spectral features near the Fermi edge, resulting from the PGM instrument function, would be of the order of 1meV. All measurements presented were taken at a constant temperature of 15K and thus standard temperature dependent effects may be neglected. The binding energy was referenced with a Pt Fermi level. The intensity was normalized to the mesh current at each data point to account for synchrotron beam decay and, after that, to the background intensity from higher order light giving rise to secondary emission above E F (as a means of normalize between different angles).

USb2 is an antiferromagnet below 200K with a tetragonal layered Cu2Sb-type structure (a = 4.270Å, c = 8.784 Å). This kind of structure allows cleaving with very little surface damage. Samples were cleaved under ultra-high vacuum (UHV) conditions to give smooth and flat surfaces for angle-resolved photoemission studies. Before introduction into the UHV photoemission chamber (p ? 10-11Torr) the orientation of the sample was determined by X-ray diffraction. The high quality of the sample was confirmed by Laue patterns and by an extremely sharp photoemission peak near the Fermi level. PES spectra were measured using an angle-resolved analyzer with ±10 acceptance angle. The momentum resolution at hν = 30 eV is about 0.09 Å-1, which is between 6.1% and 12.5% of the USb2 Brillouin zone depending on the direction of investigation. The full width at half maximum (FWHM) of this peak in normal emission PES spectra taken at 34 eV photon energy and at 15K (Fig.1) is about 24 meV and increases to 49 meV for hν = 60 eV. The increase of FWHM between photon energy

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