Structure of spin excitations in heavily electron-doped Li0.8Fe0.2ODFeSe superconductors

TL;DR

This study investigates the spin excitation structure in heavily electron-doped Li$_{0.8}$Fe$_{0.2}$ODFeSe superconductors using neutron scattering, revealing complex magnetic resonances that may be key to understanding their high transition temperature.

Contribution

It provides the first detailed characterization of spin excitations in HEDIS superconductors, highlighting their unique energy-dependent momentum structure and similarities to hole-doped cuprates.

Findings

Nearly ring-shaped magnetic resonances at 21 meV

Diamond-shaped spin excitations dispersing outward and inward

Spin excitation features analogous to hole-doped cuprates

Abstract

Heavily electron-doped iron-selenide (HEDIS) high-transition-temperature (high-$T_{\rm{c}}$) superconductors, which have no hole Fermi pockets, but have a notably high $T_{\rm{c}}$, have challenged the prevailing $s$$_\pm$ pairing scenario originally proposed for iron pnictides containing both electron and hole pockets. The microscopic mechanism underlying the enhanced superconductivity in HEDIS remains unclear. Here, we used neutron scattering to study the spin excitations of the HEDIS material Li$_{0.8}$Fe$_{0.2}$ODFeSe ($T_{\rm{c}}$ = 41 K). Our data revealed nearly ring-shaped magnetic resonant excitations surrounding ($\pi$, $\pi$) at $\sim$ 21 meV. As the energy increased, the spin excitations assumed a diamond shape, and they dispersed outward until the energy reached $\sim$ 60 meV and then inward at higher energies. The observed energy-dependent momentum structure and twisted dispersion of spin excitations near ($\pi$, $\pi$) are analogous to those of hole-doped cuprates in several aspects, thus implying that such spin excitations are essential for the remarkably high $T_{\rm{c}}$ in these materials.