[mu]SR studies of the metallic alkali fullerides

• Main Author: MacFarlane, W. Andrew
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8562

Results of muon spin rotation (μ-SR) in the metallic intercalated C₆₀ compounds (AnC₆₀, where An are n alkali metal atoms) are presented. Except for the case of K₁C₆₀, the metallic state of these systems is unstable at low temperature (to a superconducting transition in A₃C₆₀ and a magnetic metal insulator transition in A₁C₆₀)- In A₃C₆₀, the properties of the metallic and superconducting states are investigated using i) diamagnetic muons to probe the distribution of internal magnetic field and ii) paramagnetic muonium (Mu) trapped within the C₆₀ cage to probe the electronic excitations. Mu is found to exhibit strong T₁ relaxation due to its interaction with the conduction electrons. In the superconducting state this relaxation rate exhibits a small enhancement (Hebel-Slichter coherence peak) which possesses an anomalously strong magnetic field supression. Exponential temperature dependence of the relaxation rate at low reduced temperature is observed, and from this estimates of the superconducting energy gap are obtained. At very low reduced temperature, deviations from this behaviour are found. Estimates of the magnetic penetration depth from broadening of the diamagnetic precession signal in the vortex state are also presented and discussed. In A₁C₆₀ (A = Rb and Cs), the magnetic state is investigated with zero field μ-SR. Observation of a small rapidly damped oscillation below 2K in Cs₁C₆₀ is the first evidence from μ-SR of magnetic order in these materials. The relaxation at higher temperature indicates that the internal fields are static and possess a broad distribution, indicating a highly disordered static magnetic structure. From the magnitude of the zero field relaxation rates, estimates of the magnitude of the internal field are made. === Science, Faculty of === Physics and Astronomy, Department of === Graduate