Direct measurement of polaron binding energy in AMnO₃ as a function of the A site ionic size by photoinduced IR absorption

Photoinduced IR absorption was measured in undoped (LaMn)_{1-\delta}O_{3} and (NdMn)_{1-\delta}O_{3}. We observe broadening and a ~44% increase of the midinfrared anti-Jahn-Teller polaron peak energy when La^{3+} is replaced with smaller Nd^{3+}. The absence of any concurent large frequency shifts of the observed PI phonon bleaching peaks and the Brillouin-zone-center internal perovskite phonon modes measured by Raman and infrared spectroscopy indicate that the polaron peak energy shift is mainly a consequence of an increase of the electron phonon coupling constant with decreasing ionic radius <r_{A}> on the perovskite A site. This indicates that the dynamical lattice effects strongly contribute to the electronic band narrowing with decreasing <r_{A}> in doped giant magnetoresistance manganites.