Ultrafast quenching of electron-boson interaction and superconducting   gap in a cuprate superconductor
  Ultrafast spectroscopy is an emerging technique with great promise in the study of quantum materials, as it makes it possible to track similarities and correlations that are not evident near equilibrium. Thus far, however, the way in which these processes modify the electron self-energy---a fundamental quantity describing many-body interactions in a material---has been little discussed. Here we use time- and angle-resolved photoemission to directly measure the self-energy's ultrafast response to near-infrared photoexcitation in high-temperature cuprate superconductor. Below the superconductor's critical temperature, ultrafast excitations trigger a synchronous decrease of electron self-energy and superconducting gap, culminating in a saturation in the weakening of electron-boson coupling when the superconducting gap is fully quenched. In contrast, electron-boson coupling is unresponsive to ultrafast excitations above the superconductor's critical temperature and in the metallic state of a related material. These findings open a new pathway for studying transient self-energy and correlation effects in solids. 
Wentao Zhang, C. Hwang, C. L. Smallwood, T. L. Miller, G. Affeldt, K.   Kurashima, C. Jozwiak, H. Eisaki, T. Adachi, Y. Koik...
cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el