Electronic states of charge-ordering Nd0.5Sr0.5MnO3 probed by photoemission

Electronic structures of the charge-ordering manganite Nd1-xSrxMnO3 (x simi lar to 0.5) have been studied by resonant and high-resolution photoemission . The Mn 2p (Nd 3d) resonant photoemission confirmed the Mn 3d (Nd 4f) stat es hybridized with the O 2p states. The high-resolution Mn 3p resonance spe ctra show a clear transition from the metal to the charge-orderod insulator for x = 0.5 upon cooling while a Fermi cutoff is seen for x = 0.47 at all temperatures, suggesting that the transition is induced by a subtle competi tion between the charge-ordering instability and the double-exchange intera ction. Temperature and filling dependence of the spectra implies that the e lectronic states change not gradually but suddenly at the phase boundary.