Quantum critical behavior induced by Mn impurity in CuGeO3

The results of high frequency (60–315 GHz) studies of the electron spin resonance (ESR) in CuGeO3 single crystals containing 0.9% of the Mn impurity are reported. The quantitative ESR line shape analysis shows that the low-temperature (T<40 K) magnetic susceptibility of Cu2+ chains diverges as χ∼1/Tα with the critical exponent α=0.81±0.03α=0.81±0.03 and therefore indicates an onset of a quantum critical (QC) regime. The scenario, in which disorder caused by the Mn impurity in quantum spin chains in CuGeO3 may lead to the co-existence of the QC regime and the spin-Peierls dimerisation, is discussed.