Role of spin-phonon and electron-phonon interactions in the phonon renormalization of (Eu1-xBix)2Ir2O7 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 (Eu1-xBix)(2)Ir2O7, for x = 0, 0.02, 0.035, 0.05, and 0.1. The temperature variation in Raman experiments spans from 4 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 semimetal (WSM) phase at low temperatures (<similar to 50 K). The Ir-O-Ir bond bending mode A(1g) (510 cm(-1)) shows anomalous softening (for x = 0.0, 0.02, 0.035, and 0.05) in the magnetically ordered AIAO state, arising primarily from the spin-phonon interaction due to the phonon modulation of the Dzyaloshinskii-Moriya spin-exchange interaction. The two stretching modes T-2g(1) (307 cm(-1)) and T-2g(2) (382 cm(-1)) harden significantly in the magnetic insulating phase. The T-2g phonons (for x = 0.0, 0.02, 0.035, and 0.05) also show anomalous temperature dependence of their mode frequencies above T-N due to strong electron-phonon coupling. The signatures of the WSM state are observed clearly in phonon renormalization <50 K (in x = 0.02) 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.