Probing the electric field-induced doping mechanism in YBa2Cu3O7 using computed Cu K-edge x-ray absorption spectra

TL;DR

This study uses computed Cu K-edge x-ray absorption spectra to analyze how different types of doping, including oxygen vacancies and electrostatic doping, affect the electronic structure of YBa2Cu3O7, shedding light on the doping mechanism during gating.

Contribution

It provides a detailed analysis of the electronic structure changes due to various doping mechanisms in YBa2Cu3O7 using computed spectra and supports the chain-vacancy doping model.

Findings

Oxygen vacancies in CuO chains significantly alter spectral features.

Vacancy formation energies support the chain-vacancy doping mechanism.

Oxygen ordering and Hubbard U corrections influence spectral interpretations.

Abstract

We recently demonstrated that the superconductor-to-insulator transition induced by ionic liquid gating of the high temperature superconductor YBa2Cu3O7 (YBCO) is accompanied by a deoxygenation of the sample [Perez-Munoz et al., PNAS 114, 215 (2017)]. DFT calculations helped establish that the pronounced changes in the spectral features of the Cu K-edge absorption spectra measured in situ during the gating experiment arise from a decrease of the Cu coordination within the CuO chains. In this work, we provide a detailed analysis of the electronic structure origin of the changes in the spectra resulting from three different types of doping: i) the formation of oxygen vacancies within the CuO chains, ii) the formation of oxygen vacancies within the CuO2 planes and iii) the electrostatic doping. For each case, three stoichiometries are studied and compared to the stoichiometric YBa2Cu3O7, i.e YBa2Cu3O6.75, YBa2Cu3O6.50 and YBa2Cu3O6.25. Computed vacancy formation energies further support the chain-vacancy mechanism. In the case of doping by vacancies within the chains, we study the effect of oxygen ordering on the spectral features and we clarify the connection between the polarization of the x-rays and this doping mechanism. Finally, the inclusion of the Hubbard U correction on the computed spectra for antiferromagnetic YBa2Cu3O6.25 is discussed.