Inhomogeneous spin excitations in weakly coupled spin-
12
 chains
L. Shen, E. Campillo, O. Zaharko, P. Steffens, M. Boehm, K. Beauvois, B. Ouladdiaf, Z. He, D. Prabhakaran, A. T. Boothroyd, and E. Blackburn Division of Synchrotron Radiation Research, Lund University, SE-22100 Lund, Sweden Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble Cedex 9, France State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China Department of Physics, University of Oxford, Clarendon Laboratory, Oxford, OX1 3PU, United Kingdom