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

摘要

We have performed high-resolution angle-resolved photoemission spectroscopyon single-layered cuprate Bi$_2$Sr$_2$CuO$_6$ to clarify the origin of thepseudogap. By using various photon energies, we have succeeded in directlyobserving two different pseudogaps with two different energy scales whichcoexist in the antinodal region: one reflects the $d_{x^2-y^2}$-wave pairingstrength while the other has a larger energy scale suggesting an origindistinct from superconductivity. The observed two-pseudogap behavior provides akey to fully understand the pseudogap phenomena in cuprates.