Muon spin rotation/relaxation/resonance in solids

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Positively charged muons (an unstable form of antimatter produced at the TRIUMF accelerator) have several exotic properties which allow them to be used to probe the electromagnetic properties of materials using techniques known as Muon Spin Rotation/Relaxation/Resonance (µSR). The only µSR facility in the Americas (and one of only two of its kind in the world) is supported by NSERC at TRIUMF, where I strive to develop and improve µSR methods and capabilities applicable to my main physics interests: Since high temperature superconductors (HTSC) were discovered in 1986-87, µSR has been an essential probe of their properties; its unique sensitivity to weak and disordered magnetism allows us to study the coexistence of magnetism and superconductivity in these important new materials, to help understand how such things can exist and to better understand their electromagnetic properties so that their use in practical devices may be hastened. As a member of the CIAR Quantum Materials program I have learned that many of the magnetic properties of HTSC are governed by the cooperative behaviour of strongly correlated electrons, which is also manifest in the magnetism of other materials, such as cobalt oxides which are candidate materials for thermoelectric devices to convert heat directly into electricity. I collaborate with Japanese scientists to study such potential applications; I also have an ongoing collaboration with Russian scientists to study insulators and semiconductors, in which a muonium (Mu) atom is often formed when a positive muon captures an electron liberated by its passage. By studying the field dependence of Mu formation, we have been able to determine the mobility of charge carriers in various materials - information vital to their use in devices. Recently we have combined the above µSR methods to study magnetic semiconductors - candidate materials for "spintronics" devices which could perform electronic logic operations and store magnetic information simultaneously. The techniques of µSR can also be applied to various fundamental physics investigations; I am active in several of these at TRIUMF, including the TWIST experiment and several studies of muonic atoms.