Electronic structure of pyrochlore Cd₂Re₂O ₇

Detailed band structure calculations have been performed for Cd ₂Re₂O₇ in high-, middle-and low-temperature (T) phases. The calculations are based on the observed lattice structures from x-ray diffraction measurements. The spin-orbit interaction is incorporated self-consistently in both the generalized gradient approximation (GGA) and the GGA plus Hubbard U (GGA+U) approaches. It is found that the on-site U has negligible effects on the Re5d band structures; therefore both the GGA and GGA+U Re5d band energies agree well with the observed O K-edge x-ray absorption spectroscopy (XAS) spectrum, whereas the Cd4d band energy observed from photoemission spectroscopy can only be correctly reproduced by GGA+U calculations, indicating the relatively itinerant Re5d and localized Cd4d electrons. On the other hand, the spin-orbit coupling gives rise to nontrivial spin and orbital magnetic moments for the middle- T phase. Most unexpectedly, we found that the low- T phase exhibits quasi-two-dimensional Fermi surfaces. The calculated carrier numbers for the three phases are, at least qualitatively, consistent with the measured Hall coefficient.