Implanted muon spin spectroscopy on 2-O-adamantane: A model system that mimics the liquid−→glasslike transitions

The transition taking place between two metastable phases in 2-O-adamantane, namely the F m3̄m cubic, rotator phase and the lower temperature P 21/c, Z = 4 substitutionally disordered crystal is studied by means of muon spin rotation and relaxation techniques. Measurements carried out under zero, weak transverse and longitudinal fields reveal a temperature dependence of the relaxation parameters strikingly similar to those exhibited by structural glass−→liquid transitions (Bermejo et al. Phys. Rev. B 70, 214202 (2004); Cabrillo et al. Phys. Rev. B 67, 184201 (2003)). The observed behaviour manifests itself as a square root singularity in the relaxation rates pointing towards some critical temperature which for amorphous systems is located some tens of degrees above that shown as the characteristic transition temperature if studied by thermodynamic means. The implications of such findings in the context of current theoretical approaches concerning the canonical liquid-glass transition are discussed.