Nonresonant microwave absorption study of intrinsic Josephson coupling in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ single crystals

The results of nonresonant microwave absorption (NRMA) studies in Bi2212 single crystals for the H∥c axis and H∥ab plane are reported. In the former orientation, over a few degrees below ${\mathit{T}}_{\mathit{c}}$, the NRMA signal shapes evolve continuously as a function of temperature. We interpret these results as indicative of rapid strengthening of Josephson coupling between the pancake vortices in the ${\mathrm{CuO}}_2$ bilayers on cooling below ${\mathit{T}}_{\mathit{c}}$. For H∥ab there is almost no change in the signal shape in the temperature range studied. In this case, no loss component attributable to Josephson coupling is observed. © 1996 The American Physical Society.