Shallow core levels, or how to determine the doping and $T_c$ of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and Bi$_{2}$Sr$_2$CuO$_{6+\delta}$ without cooling

TL;DR

This study demonstrates that the doping level and critical temperature of Bi-based cuprate superconductors can be accurately determined at room temperature using Bi 5d core-level binding energy measurements, simplifying experimental procedures.

Contribution

The paper introduces a method to determine doping and $T_c$ from Bi 5d core-levels at room temperature, avoiding the need for cooling during measurements.

Findings

Doping level $p$ correlates with Bi 5d core-level binding energy.

Superconducting transition temperature $T_c$ can be inferred from core-level shifts.

Method enables non-invasive, room-temperature characterization of cuprates.

Abstract

Determining the doping level in high-temperature cuprate superconductors is crucial for understanding the origin of superconductivity in these materials and for unlocking their full potential. However, accurately determining the doping level remains a significant challenge due to a complex interplay of factors and limitations in various measurement techniques. In particular, in Bi$_{2}$Sr$_2$CuO$_{6+\delta}$ and Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, where the mobile carriers are introduced by non-stoichiometric oxygen $\delta$, the determination has been extremely problematic. Here, we study the doping dependence of the electronic structure of these materials in angle-resolved photoemission and find that both the doping level, $p$, and the superconducting transition temeprature, $T_c$ can be precisely determined from the binding energy of the Bi $5d$ core-levels. The measurements can be performed at room temperature, enabling the determination of $p$ and $T_c$ without cooling the samples. This should be very helpful for further studies of these materials.