Magneto-optical Kerr-effect study of the high-field superconductors Eu1−xPbxMo6S8 and Eu1−xSnxMo6S8−ySey

Abstract

A magneto-optical study on high-field superconductors is presented. We have investigated the four Chevrel-phase compounds PbMo6S8, EuMo6S8, Eu0.5Pb0.5Mo6S8, and Eu0.75Sn0.25Mo6S7.6Se0.4 in fields up to 120 kOe and temperatures down to 0.5 K. From our optical data we conclude that all these compounds are poor metals with rather few free carriers having effective masses of the order of 10me. Up to 12 eV, the real part σ1xx of the optical conductivity is dominated by Mo d⇆S p transitions. Agreement is found between σ1xx and the value of σ1xxtheor that has been derived from a self-consistent band-structure calculation. In the magneto-optical spectra two dominant Eu2+ 4f→5d transitions have been found, a 4f→5deg transition at 2.3 eV and a 4f→5t2g transition at 3.2 eV. A detailed comparison with the europium monochalcogenides yields a 60% smaller radial overlap integral of the Eu2+ 4f and 5d wave functions in the europium Chevrel phases than in the europium monochalcogenides. A strong deviation from a Brillouin function is found in the Kerr rotation at the energy of the Eu2+ 4f→5d transitions as a function of magnetic field at temperatures below 5 K. This deviation is due to another transition, which involves spin-polarized Mo d states and which we assign to Mo d→S p transitions by consideration of the line shape and the sign of its magneto-optical contribution. From the field dependence we conclude that at most a small part of the spin polarization of the conduction band behaves as a function of field as predicted by the Jaccarino-Peter compensation effect.

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