Local Electronic Structure of Interstitial Hydrogen in Iron Disulfide

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 ($\ddot{I}{‰}_{\mathrm{hf}}$). A body of evidence indicates that one muon is situated at the center of an iron-cornered tetrahedron with nearly isotropic $\ddot{I}{‰}_{\mathrm{hf}}$ (Mu${}_{\mathrm{p}}$), and that the other exists as a diamagnetic state (Mu${}_{\mathrm{d}}$, $\ddot{I}{‰}_{\mathrm{hf}}\simeq 0$). Their response to thermal agitation indicates that the Mu${}_{\mathrm{d}}$ center accompanies a shallow level (donor or acceptor) understood by effective mass model while the electronic structure of Mu${}_{\mathrm{p}}$ center is more isolated from host than Mu${}_{\mathrm{d}}$ 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${}_{\mathrm{p}}$ leading to formation of a complex defect state (Mu${}_{\mathrm{d}}^{\ast }$, $T\le 100$ K) or to motional narrowing state (Mu${}_{\mathrm{p}}^{\ast }$, $T\ge 150$ K) is also discussed.

6 pages, 5 figures