Local Electronic Structure of Interstitial Hydrogen in Iron Disulfide

TL;DR

This study uses muon spectroscopy to investigate how interstitial hydrogen acts as an electronically active impurity in FeS$_2$, revealing different defect states and diffusion behaviors that influence the material's electronic properties.

Contribution

It provides new insights into the electronic states and diffusion mechanisms of interstitial hydrogen in FeS$_2$ using muon-based experimental techniques.

Findings

Muons form two distinct defect centers with different hyperfine parameters.

One defect acts as a shallow level, the other as a deeper donor.

Evidence suggests fast diffusion and complex defect formation at low temperatures.

Abstract

The electronic structure of interstitial hydrogen in a compound semiconductor FeS$_2$ (naturally $n$-type) is inferred from a muon study. An implanted muon (Mu, a pseudo-hydrogen) forms electronically different defect centers discerned by the hyperfine parameter ($\omega_{\rm hf}$). A body of evidence indicates that one muon is situated at the center of an iron-cornered tetrahedron with nearly isotropic $\omega_{\rm hf}$ (Mu$_{\rm p}$), and that the other exists as a diamagnetic state (Mu$_{\rm d}$, $\omega_{\rm hf}\simeq 0$). Their response to thermal agitation indicates that the Mu$_{\rm d}$ center accompanies a shallow level (donor or acceptor) understood by effective mass model while the electronic structure of Mu$_{\rm p}$ center is more isolated from host than Mu$_{\rm d}$ to form a deeper donor level. These observations suggest that interstitial hydrogen also serves as an electronically active impurity in FeS$_2$. Based on earlier reports on the hydrogen diffusion in FeS$_2$, possibility of fast diffusion for Mu$_{\rm p}$ leading to formation of a complex defect state (Mu$^*_{\rm d}$, $T\le 100$ K) or to motional narrowing state (Mu$^*_{\rm p}$, $T\ge 150$ K) is also discussed.