Low energy spin excitations were investigated in the static stripe phase of La_{2-x}Sr_xCuO_4 using elastic and inelastic neutron scattering on single crystals. For x = 1/8 in which long-range static stripe order exists, an energy gap of E_g = 4 meV exists in the excitation spectrum in addition to strong quasi-elastic, incommensurate spin fluctuations associated with the static stripes. When x increases, the spectral weight of the spin fluctuations shifts from the quasi-elastic continuum to the excitation spectrum above E_g. The dynamic correlation length as a function of energy and the temperature evolution of the energy spectrum suggest a phase separation of two distinct magnetic phases in real space.
@article{arxiv.0804.3041,
title = {Hidden quantum spin gap state in the static stripe phase of La$_{2-x}$Sr$_{x}$CuO$_{4}$},
author = {M. Kofu and S. -H. Lee and M. Fujita and H. -J. Kang and H. Eisaki and K. Yamada},
journal= {arXiv preprint arXiv:0804.3041},
year = {2009}
}