Possible 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 nontrivial and strongly correlated states of matter. Here, we observe a magnetically driven phase transition between the topological Weyl semimetal and a Luttinger semimetal with quadratic band touching in ${\mathrm{Nd}}_2{\mathrm{Ir}}_2{O}_7$ using Raman scattering. We also find evidence of quadratic band touching in ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{O}_7$, with the chemical potential further away from the node. 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.