Direct electronic structure measurements of a variety of colossal magnetoresistive (CMR) oxides show the presence of a pseudogap at the Fermi energy $E_F$ which drastically suppresses the electron spectral function at $E_F.$ The pseudogap is a strong function of the layer number of the samples (sample dimensionality) and is strongly temperature dependent, with the changes beginning at the ferromagnetic transition temperature $T_c.$ These trends are consistent with the major transport trends of the CMR oxides, implying a direct relationship between the pseudogap and transport, including the “colossal” conductivity changes which occur across $T_c.$ The k dependence of the temperature-dependent effects indicates that the pseudogap observed in these compounds is not due to the extrinsic effects proposed by Joynt.

• Received 15 November 1999

DOI:https://doi.org/10.1103/PhysRevB.62.1039