Spin gap in the hole-doped spin ladder system (Sr2.5Ca11.5)Cu2O41: Neutroninelastic scattering study

The spin liquid state in the hole-doped two-leg ladder system (Sr2.5Ca11.5) Cu24O41, which exhibits unique superconductivity under high pressure, has b een studied by neutron inelastic scattering at ambient pressure. The spin g ap energy for the ladder is found to be 32.1 +/- 0.3 meV, which is still al most the same as that of the parent material Sr14Cu24O41. From the observed dispersion relation, the exchange coupling is roughly estimated at J(paral lel to) similar to 90 +/- 15 meV (along the ladders) and J(perpendicular to ) similar to 65 +/- 10 meV (along the rungs). The coupling constant J(paral lel to) is slightly decreased from that obtained for the parent compound. [ S0031-9007(98)08261-1].