Non-fermi liquid signatures of quadratic band touching and phonon anomalies in metallic Pr2Ir2O7

A single Fermi node in Pr2Ir2O7 protected by time reversal and inversion symmetry resulting from an interplay between strong electronic correlations and spin-orbit coupling (SOC) has attracted significant attention. Here, we report a detailed temperature-dependent Raman study of the ”quadratic band touching Luttinger semimetal” Pr2Ir2O7. In addition to phonons, we observe an underlying flat electronic continuum due to electronic Raman scattering (ERS) that is dominant below a characteristic temperature TQ. The observed ERS is understood using the Raman susceptibility of a non-Fermi liquid expected in a quadratic band touching system.The phonon frequencies and linewidths show anomalous temperature dependence below TQ ∼ 150 K attributed to strong electron-phonon coupling (EPC) in a quadratic band touching (QBT) state. The Ir-O-Ir bending Eg mode shows pronounced Fano asymmetry as well as anomalous linewidth broadening below TQ. Further, a Raman line at ∼460 cm−1 involving crystal field transition couples strongly to the T2g phonon at ∼350 cm−1. Our results establish the enhanced scale of electron-electron correlations and electron-phonon coupling in the QBT state of metallic Pr2Ir2O7.