Longitudinal muon spin relaxation in metals and semimetals and the Korringa law

The longitudinal muon spin relaxation in metals and semimetals is suggestiv e of a form of Korringa relaxation in which the hyperfine interaction betwe en the muons and the conduction electrons plays a dominant role. We give an alternative derivation of the Korringa law and show how muons may thus be used to study interactions with conduction electrons at interstitial sites. The alternative derivation links the topic to the use of implanted muons b oth as probes of magnetic and correlated-electron systems and as proton ana logues, modelling the behaviour of hydrogen impurity in metals and semimeta ls.