Two pseudogaps with different energy scales at the antinode of the   high-temperature Bi$_2$Sr$_2$CuO$_6$ superconductor using angle-resolved   photoemission spectroscopy
  We have performed high-resolution angle-resolved photoemission spectroscopy on single-layered cuprate Bi$_2$Sr$_2$CuO$_6$ to clarify the origin of the pseudogap. By using various photon energies, we have succeeded in directly observing two different pseudogaps with two different energy scales which coexist in the antinodal region: one reflects the $d_{x^2-y^2}$-wave pairing strength while the other has a larger energy scale suggesting an origin distinct from superconductivity. The observed two-pseudogap behavior provides a key to fully understand the pseudogap phenomena in cuprates. 
K. Nakayama, T. Sato, Y.-M. Xu, Z.-H. Pan, P. Richard, H. Ding, H.-H.   Wen, K. Kudo, T. Sasaki, N. Kobayashi, and T. Takahashi
cond-mat.supr-con cond-mat.str-el