Ab-initio Studies of (Li$_{0.8}$Fe$_{0.2}$)OHFeSe Superconductors: Revealing the Dual Roles of Fe$_{0.2}$ in Structural Stability and Charge Transfer

TL;DR

This study uses density functional theory to analyze (Li$_{0.8}$Fe$_{0.2}$)OHFeSe, revealing how Fe$_{0.2}$'s dual roles enhance structural stability and charge transfer, contributing to high-temperature superconductivity.

Contribution

The paper provides a detailed first-principles analysis of Fe$_{0.2}$'s dual role in stabilizing structure and facilitating charge transfer in FeSe-based superconductors.

Findings

Fe$_{0.2}$'s substitution strengthens interlayer attraction.

Fe$_{0.2}$ enhances interlayer charge transfer.

System favors collinear antiferromagnetic order in FeSe layers.

Abstract

The recently discovered (Li$_{0.8}$Fe$_{0.2}$)OHFeSe superconductor provides a new platform for exploiting the microscopic mechanisms of high-$T_c$ superconductivity in FeSe-derived systems. Using density functional theory calculations, we first show that substitution of Li by Fe not only significantly strengthens the attraction between the (Li$_{0.8}$Fe$_{0.2}$)OH spacing layers and the FeSe superconducting layers along the \emph{c} axis, but also minimizes the lattice mismatch between the two in the \emph{ab} plane, both favorable for stabilizing the overall structure. Next we explore the electron injection into FeSe from the spacing layers, and unambiguously identify the Fe$_{0.2}$ components to be the dominant atomic origin of the dramatically enhanced interlayer charge transfer. We further reveal that the system strongly favors collinear antiferromagnetic ordering in the FeSe layers, but the spacing layers can be either antiferromagnetic or ferromagnetic depending on the Fe$_{0.2}$ spatial distribution. Based on these understandings, we also predict (Li$_{0.8}$Co$_{0.2}$)OHFeSe to be structurally stable with even larger electron injection and potentially higher $T_c$.