First-principles study of the electronic and optical properties of Ho$_{\rm W}$ impurities in tungsten disulfide

TL;DR

This study uses first-principles calculations to explore how Holmium impurities affect the electronic and optical properties of single-layer tungsten disulfide, revealing stable impurity states and optical resonances consistent with experiments.

Contribution

It provides a detailed first-principles analysis of Ho impurities in WS2, including stability, magnetic moments, impurity states, and optical properties, which was not previously characterized.

Findings

Ho impurities are stable in WS2 with a magnetic moment of 4.75μ_B.

Localized impurity states with f-orbital character are introduced by Ho impurities.

Optical resonances match experimental data and follow group theory selection rules.

Abstract

The electronic and optical properties of single-layer (SL) tungsten disulfide (WS$_2$) in the presence of substitutional Holmium impurities (Ho$_{\rm W}$) are studied. Although Ho is much larger than W, density functional theory (DFT) including spin-orbit coupling is used to show that Ho:SL WS$_2$ is stable. The magnetic moment of the Ho impurity is found to be 4.75$\mu_B$ using spin-dependent DFT. The optical selection rules identified in the optical spectrum match exactly the optical selection rules derived by means of group theory. The presence of neutral Ho$_W$ impurities gives rise to localized impurity states (LIS) with f-orbital character in the band structure. Using the Kubo-Greenwood formula and Kohn-Sham orbitals we obtain atom-like sharp transitions in the in-plane and out-of-plane components of the susceptibility tensor, Im$\chi_{\parallel}$ and Im$\chi_{\perp}$. The optical resonances are in good agreement with experimental data.