Spin Polarons in Strongly Correlated Electron Materials

In insulators and semiconductors, the positive muon can bind an electron to form a muonium atom due to Coulomb interaction. In a strongly correlated system, the exchange interaction between free electrons and localized spins creates another channel for electron localization — the charge carrier localizes into a ferromagnetic “droplet” on the scale of the lattice spacing — a spin polaron. Here we show examples of spin polaron formation in strongly correlated electron materials detected by the muon spin rotation technique.