High-resolution photoemission spectro-scopy for the layered antiferromagnetic (La_1-zNd_z)_0.46Sr_0.54MnO₃

High-resolution HeI photoemission spectroscopy (UPS), Mn 2p-3d resonant photoemission spectroscopy (RPES) and Mn 2p X-ray absorption spectroscopy (XAS) have been performed to investigate the electronic structure and its effect on the electrical resistivity in (La_1-zNd_z)_0.46Sr_0.54MnO₃ (z = 0, 0,2, 0.6 and 1.0). It was found that in the UPS and RPES spectra the Fermi edge persisted over the temperature range 15 ≤ T ≤ 340 K regardless of the magnetic structure or the composition of the samples. The density of states at the Fermi level [N(E_F)] in the samples where 0 ≤ z ≤ 0.6 was increased drastically at the Curie temperature (T_C) with decreasing temperature, but essentially kept unchanged across the Néel temperature (T_N). A fairly large reduction at T_C and a small increase at T_N in the electrical resistivity with decreasing temperature are found to be well accounted for in terms of the temperature dependence of N(E_F). The presence of a finite N(E_F) in the insulating Nd_0.46Sr_0.54MnO₃ was also found. Thus the origin of the insulating behavior in this sample can be regarded as the Anderson localization associated with the small density of states and the chemical disorder between Nd and Sr.