Role of spin-phonon and electron-phonon interactions in phonon renormalization of (Eu$_{1-x}$Bi$_x$)$_2$Ir$_2$O$_7$ across the metal-insulator phase transition: Temperature-dependent Raman and X-ray studies

We report temperature-dependent Raman scattering and X-ray diffraction studies of pyrochlore iridates, (Eu $_{1 - x}$ Bi $_{x}$ ) $_{2}$ Ir $_{2}$ O $_{7}$ , for x=0, 0.02, 0.035, 0.05 and 0.1. The temperature variation in Raman experiments spans from 4 K to 300 K, covering the metal-insulator phase transition accompanied by paramagnetic to all-in/all-out (AIAO) spin ordering (T $_{N}$ ). These systems also show a Weyl semi-metal (WSM) phase at low temperatures (below ~50 K). We show that the Ir-O-Ir bond bending mode, A $_{1 g}$ (510 cm $^{- 1}$ ), shows anomalous softening in the magnetically ordered AIAO state, arising primarily from the spin-phonon interaction due to the phonon-modulation of the Dzyaloshinskii-Moriya (DM) spin-exchange interaction. The two stretching modes, T $_{2 g}^{1}$ (307 cm $^{- 1}$ ) and T $_{2 g}^{2}$ (382 cm $^{- 1}$ ) harden significantly in the magnetic insulating phase. The T $_{2 g}$ phonons also show anomalous temperature dependence of their mode frequencies, hitherto unreported, due to strong electron-phonon coupling. The signatures of the WSM state are observed in phonon renormalization below 50 K due to strong electron-phonon interaction. Our experimental results establish strong magneto-elastic coupling below T $_{N}$ and significant electron-phonon interactions in the metallic phase above T $_{N}$ as well as in the low-temperature WSM state.

Role of spin-phonon and electron-phonon interactions in phonon renormalization of (Eu $_{1 - x}$ Bi $_{x}$ ) $_{2}$ Ir $_{2}$ O $_{7}$ across the metal-insulator phase transition: Temperature-dependent Raman and X-ray studies

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Role of spin-phonon and electron-phonon interactions in phonon renormalization of (Eu $_{1 - x}$ Bi $_{x}$ ) $_{2}$ Ir $_{2}$ O $_{7}$ across the metal-insulator phase transition: Temperature-dependent Raman and X-ray studies

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Role of spin-phonon and electron-phonon interactions in phonon renormalization of (Eu1−x1−x​Bixx​)22​Ir22​O77​ across the metal-insulator phase transition: Temperature-dependent Raman and X-ray studies

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Role of spin-phonon and electron-phonon interactions in phonon renormalization of (Eu1−x1−x​Bixx​)22​Ir22​O77​ across the metal-insulator phase transition: Temperature-dependent Raman and X-ray studies

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Role of spin-phonon and electron-phonon interactions in phonon renormalization of (Eu $_{1 - x}$ Bi $_{x}$ ) $_{2}$ Ir $_{2}$ O $_{7}$ across the metal-insulator phase transition: Temperature-dependent Raman and X-ray studies

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Role of spin-phonon and electron-phonon interactions in phonon renormalization of (Eu $_{1 - x}$ Bi $_{x}$ ) $_{2}$ Ir $_{2}$ O $_{7}$ across the metal-insulator phase transition: Temperature-dependent Raman and X-ray studies

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