Crystal Field Excitations in Raman Spectra of Pr-based Pyrochlores*

Interplay of strong electron correlations and spin-orbit coupling leads to exotic magnetic phases in rare earth pyrochlores. Here we present a study of Pr₂Ir₂O₇ and Pr₂Zr₂O₇, which show magnetic interactions but no ordering down to low temperatures [1-3]. We performed low temperature Raman scattering spectroscopy study of Pr₂Ir₂O₇ and Pr₂Zr₂O₇ single crystals to probe crystal field excitations and phonons. A comparison of crystal field excitations in these two materials reveals a splitting in the Pr³⁺ crystal field doublet at 57 meV in Pr₂Zr₂O₇, possibly originating from the magneto-elastic coupling induced vibronic state. An anomalous broadening of this crystal field excitation is observed in Pr₂Ir₂O₇. A comparison of phonon spectrum to the density functional theory calculations demonstrates an anomalous broadening/splitting of the E_g phonon mode corresponding to the Ir-O-Ir (Zr-O-Zr) bending. We discuss relevance of our findings to magnetic properties of these materials.

[1] S. Nakatsuji, et al., Phys. Rev. Lett 96.8 (2006) 087204.
[2] Y. Machida, et al., Nature 463.7278 (2010) 210.
[3] K. Kimura et al., Nat. Commun. 4 (2013) 1934