THz Vibrational Modes of Halide Double Perovskite Cs2AgBiBr6 at Band Gap Resonance

Cs₂AgBiBr₆ is a member of the halide double perovskite family with high photovoltaic efficiency. We have synthesized single crystals of Cs₂AgBiBr₆ from solution using a controlled cooling method. The THz vibrational modes near band gap resonance were investigated by temperature dependent Raman scattering, supplemented by optical transmission measurements of the band gap itself. With a 532.8 nm laser the mode at 5.36 THz shows a very strong resonance peaked at 30 K.