The ARPES Pseudogap and Anomalous Background of Underdoped BiSCO 2212 as Evidence for a Fermi Level Band Crossing

We show that the unusual observations of a pseudogap in the normal state of underdoped Bi_2Sr_2CaCu_2O_8+delta (BiSCO) using angle resolved photoemission spectroscopy (ARPES) is consistent with a new band structure for the cuprate superconductors in which the x2-y2 and z2 bands are seen to cross at the Fermi level. Limitations in the experimental method prevent the narrow 3D z2 band from being fully resolved, leading instead to a broad background with “stepfunction” character. As a consequence, the Fermi surface is mis-assigned and a pseudogap of approximately d-wave symmetry develops.