The role of interstitial hydrogen in SrCoO$_{2.5}$ antiferromagnetic insulator

TL;DR

This paper investigates how interstitial hydrogen affects the electronic and magnetic properties of SrCoO$_{2.5}$, revealing that hydrogen acts as a deep-level center but does not introduce bound electrons, maintaining the material's insulating and antiferromagnetic state.

Contribution

The study provides a detailed theoretical analysis of interstitial hydrogen in SrCoO$_{2.5}$, showing its unique trapping behavior and minimal impact on the material's insulating and magnetic properties.

Findings

Hydrogen appears as a deep-level center without bound electrons.

Doped electrons are trapped by Co ions and are spin-polarized.

The antiferromagnetic order remains largely unaffected.

Abstract

Hydrogen exhibits qualitatively different charge states depending on the host material, as nicely explained by the state-of-the-art impurity-state calculation. Motivated by a recent experiment [Nature 546, 124 (2017)], we show that the complex oxide SrCoO$_{2.5}$ represents an interesting example, in which the interstitial H appears as a deep-level center according to the commonly-used transition level calculation, but no bound electron can be found around the impurity. Via a combination of charge difference analysis, density of states projection and constraint magnetization calculation, it turns out that the H-doped electron is spontaneously trapped by a nonunique Co ion and is fully spin-polarized by the onsite Hund's rule coupling. Consequently, the doped system remains insulating, whereas the antiferromagnetic exchange is slightly perturbed locally.