Optical conductivity of the metallic pyrochlore iridate Pr₂Ir₂O₇: Influence of spin-orbit coupling and electronic correlations on the electronic structure

The synergy of strong spin-orbit coupling and electron-electron interactions gives rise to unconventional topological states, such as topological Mott insulator, Weyl semimetal, and quantum spin liquid. In this study, we have grown single crystals of the pyrochlore iridate Pr₂Ir₂O₇ and explored its magnetic, lattice dynamical, and electronic properties. While Raman spectroscopy data reveal six phonon modes confirming the cubic Fd3̄m crystal symmetry, dc magnetic susceptibility data show no anomalies and hence indicate the absence of magnetic phase transitions down to 2~K. Both temperature-dependent electric transport and optical conductivity data reveal the metallic character of Pr₂Ir₂O₇. The optical conductivity spectrum contains a mid-infrared absorption band, which becomes more pronounced with decreasing temperature due to spectral weight transfer from high to low energies. The presence of the mid-infrared band hints at the importance of correlation physics. The optical response furthermore suggests that Pr₂Ir₂O₇ is close to the Weyl semimetal phase.