Para-Meissner oscillations in the magnetization of a high-temperature superconductor

We find that the magnetization becomes positive for a given number of Josephson junctions in a sample at low magnetic fields. When the phase angle crosses nπ (n=integer) radians, the energy of the system changes sign. Accordingly, the magnetization also changes sign when the phase angle becomes 1/2 (2n+1)π. Thus we predict an unusual positive magnetization in the Meissner region of the (H, T) phase diagram of a superconductor. The experimental measurements of magnetization of Bi2Sr2CaCu2O8+δ show that it becomes positive at small fields. In some of the samples, depending on the number of Josephson junctions, the susceptibility as a function of temperature becomes a positive constant which is independent of temperature, T, at low temperatures. At large magnetic fields, the usual negative magnetization is found which corresponds to the Meissner value of the susceptibility, χ=-1/4π. (orig.)