Observation of semi-localized dispersive states in the strongly correlated electron-doped ferromagnet Eu$_{1-x}$Gd$_{x}$O

TL;DR

This study investigates semi-localized dispersive states in electron-doped EuO using spectroscopy and modeling, revealing a constant spatial extent of donor wavefunctions and insights into the semiconductor-metal transition.

Contribution

It provides new understanding of how semi-localized states evolve in lightly doped EuO, highlighting a constant donor wavefunction length scale above the Curie temperature.

Findings

Donor wavefunctions have a constant spatial extent regardless of doping level.

Semi-localized states influence the semiconductor-to-metal transition in EuO.

Results are consistent with tunneling studies and applicable to doped complex oxides.

Abstract

Chemical substitution plays a key role in controlling the electronic and magnetic properties of complex materials. For instance, in EuO, carrier doping can induce a spin-polarized metallic state, colossal magnetoresistance, and significantly enhance the Curie temperature. Here, we employ a combination of molecular-beam epitaxy, angle-resolved photoemission spectroscopy, and an effective model calculation to investigate and understand how semi-localized states evolve in lightly electron doped Eu$_{1-x}$Gd$_{x}$O above the ferromagnetic Curie temperature. Our studies reveal a characteristic length scale for the spatial extent of the donor wavefunctions which remains constant as a function of doping, consistent with recent tunneling studies of doped EuO. Our work sheds light on the nature of the semiconductor-to-metal transition in Eu$_{1-x}$Gd$_{x}$O and should be generally applicable for doped complex oxides.