Khasanov, R. (2022). Muons under pressure. In S. J. Blundell, R. De Renzi, T. Lancaster, & F. L. Pratt (Eds.), Muon spectroscopy. An introduction (pp. 313-322). Oxford University Press.
Pressure is an important thermodynamic variable in physics. Under applied pressure the interatomic distances in a material shrink, leading to changes in interatomic interactions. Investigating the response of a material to pressure allows us to probe the interplay of interactions and to determine microscopic parameters. Pressure tuning is therefore widely used to identify critical points, study phase transitions, and establish phase diagrams. In this chapter we shall discuss the requirements and challenges of performing µSR experiments under pressure and, to illustrate the discussion, we describe in detail the high-pressure facility at the Paul Scherrer Institute (PSI) in Switzerland. Gas pressure systems are then briefly discussed, before turning to some science examples and discussing the outlook for pressure studies.