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

Abstract Transmittance of the colossal magnetoresistive compound Nd 0.5 Sr 0.5 MnO 3 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 ( x 2 − y 2 )-orbital degree of freedom in the low-energy optical properties of Nd 0.5 Sr 0.5 MnO 3 and other doped manganites with planar ( x 2 − y 2 )-orbital order, as predicted theoretically. The results are discussed in terms of the orbital-liquid concept.