Selective Hybridization between Main Band and Superstructure Band in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ Superconductor

TL;DR

This study uses high-resolution ARPES to reveal unexpected hybridization between main and superstructure bands in Bi2212, affecting the Fermi surface topology and providing insights into the superstructure's origin and its role in superconductivity.

Contribution

It uncovers the hybridization phenomenon between main and superstructure bands in Bi2212, which was not observed in Bi2201, and discusses its implications for understanding the material's electronic structure.

Findings

Hybridization observed in Bi2212 but not in Bi2201.

Four bands detected instead of two at certain Fermi surface intersections.

Hybridization persists across doping levels and in both superconducting and normal states.

Abstract

High-resolution laser-based angle-resolved photoemission measurements have been carried out on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) and Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+\delta}$ (Bi2201) superconductors. Unexpected hybridization between the main band and the superstructure band in Bi2212 is clearly revealed. In the momentum space where one main Fermi surface intersects with one superstructure Fermi surface, four bands are observed instead of two. The hybridization exists in both superconducting state and normal state, and in Bi2212 samples with different doping levels. Such a hybridization is not observed in Bi2201. This phenomenon can be understood by considering the bilayer splitting in Bi2212, the selective hybridization of two bands with peculiar combinations, and the altered matrix element effects of the hybridized bands. These observations provide strong evidence on the origin of the superstructure band which is intrinsic to the CuO$_2$ planes. Therefore, understanding physical properties and superconductivity mechanism in Bi2212 should consider the complete Fermi surface topology which involves the main bands, the superstructure bands and their interactions.