Macroscopic Quantum Coherence of the Spin Triplet in the Spin-Ladder   Compound Sr14Cu24O41
  We report the direct observation by inelastic neutron scattering experiments of a spin triplet of magnetic excitations in the response associated with the ladders in the composite cuprate Sr14Cu24O41. This appears as a peak at q_{Q1D}=\pi and energy \Delta_1=32.5 meV, and we conjecture that all the triplets making up this conspicuous peak have the same phase and therefore interpret it as the signature of the occurrence of quantum coherence along the ladder direction between entangled spin pairs. From the comparison with previous neutron and x-ray data, we conclude that the temperature evolution of this mode is driven by the crystallization of holes into a charge density wave in the ladder sublattice 
Emilio Lorenzo (NEEL), L. P. Regnault (SPSMS - UMR 9001), Cyrille   Boullier (MDN), Nicolas Martin (MDN), A.H. Moudden (LLB ...
cond-mat.str-el