Microwave properties of Nd0.5Sr0.5MnO3: a key role of the (x2−y2)-orbital effects

Transmittance of the colossal magnetoresistive compound Nd0.5Sr0.5MnO3 showing metal–insulator phase transition has been studied by means of the submm- and mm-wavelength band spectroscopy. An unusually high transparency of the material provided direct evidence for the significant suppression of the coherent Drude-weight in the ferromagnetic metallic state. Melting of the A-type antiferromagnetic states has been found to be responsible for a considerable increase in the microwave transmission, which was observed at the transition from the insulating to the metallic phase induced by magnetic field or temperature. This investigation confirmed a dominant role of the (x2−y2)-orbital degree of freedom in the low-energy optical properties of Nd0.5Sr0.5MnO3 and other doped manganites with planar (x2−y2)-orbital order, as predicted theoretically. The results are discussed in terms of the orbital-liquid concept.