Negatively charged muonium as a detector of electron spin polarization; A Puzzle and a possible theory

Gu, B.; Ziman, T.*; Maekawa, Sadamichi

We explore theoretical explanations for laser pumped experiments, that have established that muonium can be a tool in spintronics for following non-equilibrium spin polarizations of the conduction electrons. In the original experiments on Si the sensitivity was argued to be due to spin exchange with the bound electron in muonium, but in GaAs an effect is seen even in the case of negatively charged muonium. This is more problematic, as spin exchange with a third electron should be weak given the spin singlet state of the two bound electrons of the negative muonium ion. We discuss a mechanism to explain the sensitivity of negatively charged muonium ions to the spin-polarization of semiconductors in terms of the coherent mixing of charge states induced by hybridization with the semiconducting host.