2 Muon Spin Rotation Spectroscopy

In the most general description Muon Spin Rotation/Relaxation/Resonance (collectively called $\mu{\cal SR}$) includes all experimental techniques that exploit the anisotropic decay of spin-polarized muons for studying materials. This covers an enormous range of fields of study, presently including various aspects of chemistry, magnetism, superconductivity, semiconductor properties and quantum diffusion. The essential ingredient common to all these experiments is that the muons interact with the material in which they have been deposited in various ways that have observable effects on their spin polarization, ultimately allowing one to extract information about the muon's environment. In order to understand how this is done we discuss the basics of muons, muon beams and details of $\mu{\cal SR}$ experiments in this chapter.