Photoemission Line shape Study on La$_{0.7}$Sr$_{0.3}$Mn$_{1-δ}$Al$_δ$O$_{3}$ ($δ$ = 0, 0.03, 0.06)

Abstract

We have studied the line shapes of ultraviolet photoemission spectra of La$_{0.7}$Sr$_{0.3}$Mn$_{1-δ}$Al$_δ$O$_3$ ($δ$ = 0, 0.03, 0.06) systems to test the extrinsic image charge screening effect on photoemission spectra recently suggested by R. Joynt (Science {\bf 284}, 777 (1999)), who argued that the photoemission spectrum near the Fermi energy, specially for poorly conducting system, can be very different from the intrinsic density of states because the outgoing electron has probability of losing its kinetic energy due to the image force. We tested this argument in real materials experimentally by measuring the photoemission line shapes of La$_{0.7}$Sr$_{0.3}$Mn$_{1-δ}$Al$_δ$O$_3$ systems, for which all the requirements of this theory are satisfied and sample resistivities change systematically. We found that experimental photoemission spectra do not show the change of line shapes expected from the extrinsic image force effect and we conclude that the influence of this long range interaction is not so large as suggested in that paper.