Quantum critical behavior induced by Mn impurity in CuGeO3

TL;DR

This study investigates how Mn impurities induce quantum critical behavior in CuGeO3, revealing a divergence in magnetic susceptibility at low temperatures and suggesting a transition into a Griffiths phase with coexisting phenomena.

Contribution

It provides experimental evidence of quantum criticality induced by impurity disorder in CuGeO3 and identifies the onset of a Griffiths phase at around 40 K.

Findings

Magnetic susceptibility diverges with a critical exponent of 0.81 below 40 K.

Transition into Griffiths phase occurs at approximately 40 K.

Disorder from Mn impurities leads to coexistence of quantum criticality and spin-Peierls dimerisation.

Abstract

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.