Time- and Momentum-resolved Gap Dynamics in Bi2Sr2CaCu2O8+delta
  We use time- and angle-resolved photoemission spectroscopy to characterize the dynamics of the energy gap in superconducting Bi2Sr2CaCu2O8+delta (Bi2212). Photoexcitation drives the system into a nonequilibrium pseudogap state: Near the Brillouin zone diagonal (inside the normal-state Fermi arc), the gap completely closes for a pump fluence beyond F = 15 {\mu}J/cm^2; toward the Brillouin zone face (outside the Fermi arc), it remains open to at least 24 {\mu}J/cm^2. This strongly anisotropic gap response may indicate multiple competing ordering tendencies in Bi2212. Despite these contrasts, the gap recovers with relatively momentum-independent dynamics at all probed momenta, which shows the persistent influence of superconductivity both inside and outside the Fermi arc. 
Christopher L. Smallwood, Wentao Zhang, Tristan L. Miller, Chris   Jozwiak, Hiroshi Eisaki, Dung-Hai Lee, and Alessandra Lanzara
cond-mat.str-el