A SOFT-X-RAY SPECTROMETER FOR RESONANT INVERSE-PHOTOEMISSION

We describe the concept and the performances of a new tunable soft x-r ay inverse photoemission (IPES) spectrometer. The instrument is based on a variable-geometry Bragg spectrograph, and it can be operated with minor modifications over a wide range of photon energies (600<hv<4000 eV). It was originally designed for IPES measurements of cerium compo unds at the Ce M(5)(3d(5/2)-->4f,hv=883 eV) absorption edge, where the Ce 4f IPES cross section is resonantly enhanced. Such resonant IPES ( RIPES) spectra, now routinely performed by this instrument, are 10-100 times more sensitive to the Ce 4f states than conventional x-ray brem sstrahlung spectra, with a comparable energy resolution (Delta E simil ar to 600 meV). We plan to exploit the wide tunability of the spectrom eter to perform RIPES measurements of other correlated materials, name ly at the Cu L(2,3)(2p-->d,hv=930 and 950 eV) edge in the high-ir, sup erconductors. (C) 1995 American Institute of Physics.