Pseudogaps and Extrinsic Losses in Photoemission Experiments on Poorly Conducting Solids

A photoelectron emitted from a conducting solid may suffer a substantial energy change through ohmic losses that can drastically alter the line shape on the millielectron volt scale that is now observable through improved resolution. Almost all of this energy loss occurs after the electron leaves the solid. These losses are expected to be important in isotropic materials with relatively low conductivity, such as certain colossal magnetoresistance manganates, and in very electrically anisotropic materials, such as one-dimensional conductors, and may also affect interpretation of photoemission in superconductors with high transition temperatures. The electric field of the photoelectron can penetrate the solid, and extrinsic losses of this type can mimic pseudogap effects and other peculiar features of photoemission in cubic manganates, as illustrated for La0.67Ca0.33MnO3.