Unusual photoemission resonances of oxygen-dopant induced states in Bi$_{2}$Sr$_2$CaCu$_2$O$_{8+x}$

TL;DR

This study investigates how oxygen dopants in Bi$_{2}$Sr$_2$CaCu$_2$O$_{8+x}$ influence photoemission spectra across various doping levels, revealing a doping-dependent impurity state linked to oxygen dopants and their interaction with copper.

Contribution

It provides new insights into the nature of oxygen-induced impurity states and their resonance behavior in high-temperature superconductor Bi$_{2}$Sr$_2$CaCu$_2$O$_{8+x}$, using angle-resolved photoemission spectroscopy.

Findings

Identification of a non-dispersive A$_{1g}$ peak scaling with doping.

Correlation of the impurity state with oxygen dopants observed by STM.

Evidence of mixing between local impurity states and Cu via apical oxygens.

Abstract

We have performed an angular-resolved photoemission study of underdoped, optimally doped and overdoped Bi$_{2}$Sr$_2$CaCu$_2$O$_{8+x}$ samples using a wide photon energy range (15 - 100 eV). We report a small and broad non-dispersive A$_{1g}$ peak in the energy distribution curves whose intensity scales with doping. We attribute it to a local impurity state similar to the one observed recently by scanning tunneling spectroscopy and identified as the oxygen dopants. Detailed analysis of the resonance profile and comparison with the single-layered Bi$_{2}$Sr$_2$CuO$_{6+x}$ suggest a mixing of this local state with Cu via the apical oxygens.