Optical control of non-equilibrium superconducting phase transition   below Tc in a cuprate
  Photoinduced phase transitions from insulating to metallic states, accompanied by structural re-arrangements, have been recently reported in complex transition-metal oxides. However, the optical control of a purely electronic phase transition, where the thermodynamic phase is determined by the distribution of excitations, has remained elusive. Here we report optical control of the electronic phase in an underdoped Bi2212 crystal through impulsive photoinjection of quasiparticles (QP) via ultrashort laser pulses, avoiding significant laser heating. An abrupt transition of the transient optical electronic response is observed at a critical fluence of Ipump=70 uJ/cm^2. We show that the measured dynamics is consistent with an inhomogenous first-order superconducting-to-normal state phase transition, triggered by a sudden shift of the chemical potential. 
Claudio Giannetti, Giacomo Coslovich, Federico Cilento, Gabriele   Ferrini, Hiroshi Eisaki, Nobuhisa Kaneko, Martin Greven a...