Anomalous pressure dependence of phonon line widths in metallic pyrochlore iridates (Eu$$_{1-x}$$Bi$$_x$$)$$_2$$Ir$$_2$$O$$_7$$: crossover from incoherent to coherent metal

• DOI: 10.1007/s12043-023-02620-2
• Publication Date: 2023-08-30T12:02:30Z
• Authors: Anoop Thomas; Prachi Telang; Dibyata Rout; Kshiti Mishra; Anand Pal; D V S Muthu; P S Anil Kumar; Surjeet Singh; A K Sood
• Keywords: Physics; 500; 530

Pyrochlore iridate (Eu 2 Ir 2 O 7) shows an interesting metallic phase, termed as incoherent metal, above the metal–insulator transition temperature, with high resistivity and positive temperature coefficient of resistivity (TCR). On increasing the pressure, there is a crossover at pressure P* to a coherent metal phase with positive TCR. We have investigated this crossover using high-pressure Raman spectroscopy and X-ray diffraction for a series of samples (Eu 1-x Bi x) 2 Ir 2 O 7 (x = 0, 0.02, 0.035 and 0.1) up to ∼ 20 GPa. X-ray diffraction data show a clear change in the pressure dependence of Ir–Ir bond distance at P*. The line width of the A 1g phonon shows an anomalous decrease with pressure up to P*, without significant change in the line width of the other three Raman modes with symmetries T2g1 , Eg and T2g2 . We attribute these results to the decreasing contribution of electron–phonon coupling in the incoherent metal till P*.