Influence of anti-site disorder and electron-electron correlations on the electronic structure of CeMnNi$_4$

TL;DR

This study combines experimental and theoretical methods to reveal how electron-electron interactions and atomic disorder influence the high spin polarization in CeMnNi4, a complex correlated material.

Contribution

It demonstrates the critical roles of Ni 3d electron correlations and Mn-Ni anti-site disorder in enhancing spin polarization, using HAXPES and density functional theory.

Findings

Anti-site disorder broadens Ni 3d minority-spin peak near E_F

Increasing U_Ni shifts the Ni 3d peak towards E_F, boosting spin polarization

Surface valence state transition highlights importance of bulk-sensitive spectroscopy

Abstract

CeMnNi$_4$ exhibits an unusually large spin polarization, but its origin has baffled researchers for more than a decade. We use bulk sensitive hard x-ray photoelectron spectroscopy (HAXPES) and density functional theory based on the Green's function technique to demonstrate the importance of electron-electron correlations of both the Ni 3$d$ ($U_{Ni}$) and Mn 3$d$ ($U_{Mn}$) electrons in explaining the valence band of this multiply correlated material. We show that Mn-Ni anti-site disorder as well as $U_{Ni}$ play crucial role in enhancing its spin polarization: anti-site disorder broadens a Ni 3$d$ minority-spin peak close to the Fermi level ($E_F$), while an increase in $U_{Ni}$ shifts it towards $E_F$, both leading to a significant increase of minority-spin states at $E_F$. Furthermore, rare occurrence of a valence state transition between the bulk and the surface is demonstrated highlighting the importance of HAXPES in resolving the electronic structure of materials unhindered by surface effects.