Role of intercalated Cobalt in the electronic structure of Co$_{1/3}$NbS$_2$

TL;DR

This study uses ARPES to explore the electronic structure of Co$_{1/3}$NbS$_2$, revealing significant deviations from the parent material due to intercalation-induced charge transfer and hybridization, indicating a strongly correlated electron system.

Contribution

First ARPES investigation of Co$_{1/3}$NbS$_2$, uncovering unique electronic features caused by intercalation and hybridization effects not seen in the parent compound.

Findings

Charge transfer shifts Fermi energy by 0.5 eV.

Discovery of a Co-origin shallow band crossing the Fermi level.

Enhanced interlayer hybridization due to intercalation.

Abstract

Co$_{1/3}$NbS$_2$ is the magnetic intercalate of 2H-NbS$_2$ where electronic itinerant and magnetic properties strongly influence each other throughout the phase diagram. Here we report the first angle-resolved photoelectron spectroscopy (ARPES) study in Co$_{1/3}$NbS$_2$. The observed electronic structure seemingly resembles the one of the parent material 2H-NbS$_2$, with the shift in Fermi energy of 0.5 eV accounting for the charge transfer of approximately two electrons from each Co ion into the NbS$_2$ layers. However, we observe significant departures from the 2H-NbS$_2$ rigid band picture: Entirely unrelated to the 2H-NbS$_2$ electronic structure, a shallow electronic band is found crossing the Fermi level near the boundary of the first Brillouin zone of the superstructure imposed by the intercalation. The evolution of the experimental spectra upon varying the incident photon energy suggests the Co origin of this band. Second, the Nb bonding band, found deeply submerged below the Fermi level at the $\Gamma$ point, indicates the interlayer-hybridization being very much amplified by intercalation, with Co magnetic ions probably acting as covalent bridges between NbS$_2$ layers. The strong hybridization between conducting and magnetic degrees of freedom suggests dealing with strongly correlated electron system where the interlayer coupling plays an exquisite role.