Quantum critical behavior induced by Mn impurity in CuGeO3
  Results of high frequency (60-315 GHz) studies of ESR in CuGeO3 single crystals containing 0.9% of Mn impurity are reported. Quantitative EPR line shape analysis allowed concluding that low temperature magnetic susceptibility for T <40 K diverges following power law with the critical exponent 0.81 and therefore manifests onset of a quantum critical (QC) regime. We argue that transition into Griffiths phase occurs at TG~40 K and disorder produced by Mn impurity in quantum spin chains of CuGeO3 may lead to co-existence of the QC regime and spin-Peierls dimerisation. 
A.V.Semeno, N.E.Sluchanko, N.A.Samarin, A.A.Pronin, H.Ohta, S.Okubo,   S.V.Demishev