INTERLAYER COUPLING IN THE SUPERCONDUCTING STATE OF BI2SR2CA2CU3O10

Spin echo double resonance has been used to detect the spin-spin coupl ing between Cu spins on adjacent CuO2 layers. These measurements, perf ormed in the superconducting state, on the three-layer Pb-doped bismut h high-ir, compound demonstrate the existence of interlayer exchange c oupling as well as interlayer correlations in the quasiparticle excita tions. An estimate of the interlayer exchange constant J(perpendicular to) is found to be 43 K, 3% of the intralayer value.