High Field ESR Study of BaCu2(Si1-xGex)2O7Single Crystal

Recent advance of a field theoretical approach of a low-temperature electron spin resonance (ESR) in S=½ antiferromagnetic chain, which has Dzyaloshinskii-Moriya (DM) interactions and staggered g-tensor sites, by Oshikawa and Affleck (OA) suggests peculiar magnetic field dependence of ESR. Although BaCu 2 (Si 1 - x Ge x ) 2 O 7 is an antiferromagnetic chain system with mixed antiferromagnetic and ferromagnetic interchain interactions, we found that x=0.65 substance shows the peculiar field dependence of ESR predicted by OA theory. The temperature dependence of the line width showed the power-law dependence and strong field dependence in the gapless spinon regime which can be well interpreted by OA theory. The temperature dependence of the resonance shift turned out to be also consistent with OA theory. These results are also discussed in connection with Cu-Benzoate which is considered as a model substance of OA theory.