Mapping the Electronic Structure of Each Ingredient Oxide Layer of High-$T_\textrm{c}$ Cuprate Superconductor Bi2Sr2CaCu2O8+{\delta}

TL;DR

This study uses cryogenic STM to map the electronic structures of all layers in Bi2Sr2CaCu2O8+δ, revealing layer-specific features that challenge existing models of high-Tc superconductivity.

Contribution

It provides the first layer-by-layer electronic structure mapping of all ingredient planes in a high-Tc cuprate superconductor, clarifying their roles in superconductivity.

Findings

Pseudogap is intrinsic to BiO planes, not directly related to Cooper pairing.

SrO planes show a Van Hove singularity near the Fermi level.

The superconducting gap is observed only in CuO2 planes and vanishes near Tc.

Abstract

Understanding the mechanism of high transition temperature (Tc) superconductivity in cuprates has been hindered by the apparent complexity of their multilayered crystal structure. Using a cryogenic scanning tunneling microscopy, we report on layer-by-layer probing of the electronic structures of all ingredient planes (BiO, SrO, CuO2) of Bi2Sr2CaCu2O8+{\delta} superconductor prepared by argon-ion bombardment and annealing technique. We show that the well-known pseudogap (PG) feature observed by STM is inherently a property of the BiO planes and thus irrelevant directly to Cooper pairing. The SrO planes exhibit an unexpected Van Hove singularity near the Fermi level, while the CuO2 planes are exclusively characterized by a smaller gap inside the PG. The small gap becomes invisible near Tc, which we identify as the superconducting gap. The above results constitute severe constraints on any microscopic model for high Tc superconductivity in cuprates.