Spectroscopic evidence for preformed Cooper pairs in the pseudogap phase   of cuprates
  Angle-resolved photoemission on underdoped La$_{1.895}$Sr$_{0.105}$CuO$_4$ reveals that in the pseudogap phase, the dispersion has two branches located above and below the Fermi level with a minimum at the Fermi momentum. This is characteristic of the Bogoliubov dispersion in the superconducting state. We also observe that the superconducting and pseudogaps have the same d-wave form with the same amplitude. Our observations provide direct evidence for preformed Cooper pairs, implying that the pseudogap phase is a precursor to superconductivity. 
M. Shi, A. Bendounan, E. Razzoli, S. Rosenkranz, M. R. Norman, J. C.   Campuzano, J. Chang, M. Mansson, Y. Sassa, T. Claesso...