Infrared Absorption from Charge Density Waves in Magnetic Manganites

The infrared absorption of charge density waves coupled to a magnetic background is first observed in two manganites La_1-xCaₓMnO₃ with x0ex0ex=0ex0ex0.5 and x0ex0ex=0ex0ex0.67. In both cases a BCS-like gap 2Δ(T), which for x0ex0ex=0ex0ex0.5 follows the hysteretic ferromagnetic-antiferromagnetic transition, fully opens at a finite T₀<TN, with 2Δ(T₀)/kBTc5. These results may also explain the unusual coexistence of charge ordering and ferromagnetism in La0.5Ca0.5MnO₃.