Photoexcitations inLa2CuO4: 2-eV energy gap and long-lived defect states

Abstract

We report the photoinduced optical-absorption spectrum of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$. Two photoinduced absorptions are observed, peaking at 0.5 and at 1.4 eV, with a crossover to photoinduced bleaching above 2.0 eV. These data, together with observed luminescence at ∼2 eV, confirm the presence of an energy gap at or above this energy, as well as the existence of long-lived stable electronic defect states in this system.