Screening in YBCO at large wave vectors

TL;DR

This study combines experimental IXS and ab initio TDDFT to investigate electronic screening in YBCO, revealing strong core-electron interactions and suggesting correlation effects beyond current theoretical descriptions.

Contribution

It provides a detailed comparison of IXS and TDDFT results in YBCO, highlighting new excitations related to Ba electrons and the potential role of correlations in antiscreening phenomena.

Findings

Strong interaction between core electrons and valence excitations.

Excellent agreement between IXS and TDDFT results.

Identification of new excitations linked to Ba electrons.

Abstract

We present experimental inelastic x-ray scattering (IXS) and ab initio time-dependent density-functional-theory (TDDFT) studies of YBa2Cu3O7-{\delta}. The response of the low-lying Ba 5p and Y 4p core electrons is shown to interact strongly with the Cu 3d and O 2p excitations, with important consequences on screening. The agreement between IXS and TDDFT results is excellent, apart from a new type of excitations, mainly related to loosely bound Ba electrons and significantly affected by correlations. This points to correlation mechanisms not fully described by TDDFT that might have a role in giving rise to antiscreening.