Photoinduced expansion of cuprate superconductors: Evidence of strong electron-lattice coupling

Intense light pulses cause ``colossal'' (larger than thermal) expansion in cuprate films. We show that a simple ionic model accounts for both the static expansion caused by chemical doping and the photoinduced dynamic expansion. Because of the (static or intermittent) reduction of ionic charges, the ions feel lesser electrostatic attraction and move apart. The displacements can be large since the Madelung energy can change by more than 10.3em0exeV/atom. From this ionic picture, one would expect significant structural reconstruction at heterointerfaces and photoinduced shifts in Raman frequencies.