ESR of quantum spin chains with staggered fields

Abstract We study electron spin resonance (ESR) of S= 1 2 antiferromagnetic Heisenberg chain systems, Cu-benzoate and Cu-pyrimidine, with staggered fields caused by alternating g-tensor and Dzyaloshinskii–Moriya interaction. We observe clearly the effect of the staggered fields on the shift and the linewidth of ESR spectra. Especially, in Cu-benzoate, we reveal the field-induced gap and the quantum critical behavior as a dynamical crossover.