Evidence for magnetic-field-induced decoupling of superconducting bilayers in La${}_{2-x}$Ca${}_{1+x}$Cu${}_2$O${}_6$

We report a study of magnetic susceptibility and electrical resistivity as a function of temperature and magnetic field in superconducting crystals of La${}_{2-x}$Ca${}_{1+x}$Cu${}_2$O${}_6$ with $x=0.10$ and 0.15 and transition temperature $T_c^{\mathrm{m}}=54$ K (determined from the susceptibility). When an external magnetic field is applied perpendicular to the CuO${}_2$ bilayers, the resistive superconducting transition measured with currents flowing perpendicular to the bilayers is substantially lower than that found with currents flowing parallel to the bilayers. Intriguingly, this anisotropic behavior is quite similar to that observed for the magnetic irreversibility points with the field applied either perpendicular or parallel to the bilayers. We discuss the results in the context of other studies that have found evidence for the decoupling of superconducting layers induced by a perpendicular magnetic field.