Dynamical Structural Instabilities in La1.9Sr0.1CuO4 Under Intense Laser Photoexcitation

The femtosecond timescale photoinduced reflectivity response in La 1.9 Sr 0.1 CuO 4 under intense laser photoexcitation is reported as a function of intensity and temperature. We observe saturation of the response, which corresponds to the destruction of both superconducting gap and the pseudogap. We find that the saturation thresholds scale approximately as Δ 2 , where Δ = Δ S for the superconducting gap and Δ = Δ P for the pseudogap where Δ P / Δ S ≈10. The pseudogap destruction threshold correlates with the onset of a structural phase transition measured with time-resolved electron diffraction.