Raman signatures of quadratic band touching state and strong spin-phonon coupling in pyrochlore iridates (Sm1−xBix)2Ir2O7

Abstract

In this work, we report low-temperature Raman spectroscopic measurement to investigate the temperature dependence of phonons and magnetic as well as electronic excitations in (Sm1−xBix)2Ir2O7 for x=0, 0.02, 0.035, 0.05, and 0.10. A strong spin-phonon coupling induced phonon renormalization is observed below magnetic transition temperature TN for samples with x≤0.035. An underlying broad continuum attributed to pronounced spin-spin correlations is observed below TN for pure Sm2Ir2O7. Significant phonon anomalies at lower temperatures, much below TN, for x=0 and 0.02, are observed and are attributed to a possible crossover into the Weyl semimetal state. Most interestingly, we observe clear signatures of quadratic band touching in x=0.05 and 0.10 systems in terms of a broad electronic continuum at low temperatures analyzed using the Raman susceptibility for a non-Fermi liquid, corroborating the inference from recent transport measurements.