Weyl-Luttinger phase transition in pyrochlore iridates revealed by Raman scattering

Pyrochlore iridates are thought to be a fertile ground for the realization of topologically non-trivial and strongly correlated states of matter. Here we provide a compelling evidence of interacting Weyl electrons in Nd$_2$Ir$_2$O$_7$ and quadratic band touching in Pr$_2$Ir$_2$O$_7$ by Raman scattering. We observe a magnetically-driven phase transition between the topological Weyl semimetal and a Luttinger semimetal with quadratic band touching in Nd$_2$Ir$_2$O$_7$. Our theoretical analysis of the Raman scattering from Weyl and Luttinger quasiparticles agrees with experimental observations, and enables a characterization of the material parameters while revealing interaction and disorder effects through a relatively short quasiparticle lifetime.