CORRELATION-EFFECTS IN YB-4(AS0.88SB0.12)(3) AND YB-4(AS0.71SB0.29)(3)

The 4f correlations in Yb-4(As0.88Sb0.12), and Yb-4(As0.71Sb0.29)(3) g ive rise to an exceptional field-dependence of the optical reflectivit y, measured for photon energies between 3 meV and 0.8 eV at 15 K under magnetic fields up to 6 T. From the optical spectra, the energy diffe rence between the occupied and empty 4f(14) state in these materials i s estimated to be 0.42 eV. Furthermore, we have detected a strongly fi eld dependent Drude-like absorption in the far infrared and an unusual field enhancement of the phonon peaks. (C) 1998 Elsevier Science B.V. All rights reserved.