Phonon anomalies in pyrochlore iridates studied by Raman spectroscopy

We report polarization-resolved Raman scattering measurements on single crystals of the pyrochlore compound Eu 2 Ir 2 O 7 which exhibits a ground state with non-collinear magnetic order, as well as its paramagnetic counterpart Pr 2 Ir 2 O 7 . The spectra reveal the six Raman-active optical phonons expected for the pyrochlore lattice symmetry. Combined with density functional calculations, polarization analysis of the Raman intensity allows us to assign all observed peaks to speci(cid:12)c vibration patterns. Whereas most phonon pro(cid:12)les are weakly temperature dependent, an Ir-O-Ir bond-bending vibration in Eu 2 Ir 2 O 7 exhibits a pronounced Fano asymmetry in the paramagnetic state, and marked softening and lineshape anomalies at the magnetic phase transition. These observations indicate strong electron-phonon interactions, which must be considered in models of the electronic properties and phase behavior of the pyrochlore iridates. In addition, a prominent magnon mode appears in the Raman spectrum of Eu 2 Ir 2 O 7 below the magnetic transition temperature.

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