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

TL;DR

This paper presents evidence that the pseudogap observed in underdoped BiSCO 2212 is due to a band crossing at the Fermi level, caused by a new band structure involving x2-y2 and z2 bands, with experimental limitations affecting the observations.

Contribution

It introduces a new interpretation of the pseudogap in cuprates as resulting from a band crossing at the Fermi level, supported by ARPES data.

Findings

Band crossing at the Fermi level involving x2-y2 and z2 bands.

Experimental limitations cause broad background and mis-assignment of Fermi surface.

Pseudogap exhibits approximately d-wave symmetry.

Abstract

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.