Strongly nonlinear magnetization above Tc in Bi2Sr2CaCu2O8 + δ

Using high-resolution magnetometry we have investigated in detail the magnetization M above the critical temperature Tc in Bi2Sr2CaCu2O8. In a broad range of temperature T above Tc, we find that M(T,H) is strongly non-linear in the field H. We show that as T → Tc, the susceptibility χ(T,H) diverges to very large values (χ → − 1) if measured in weak H. In addition, M(H) displays an anomalous non-analytic form M ~ H1/δ in weak fields with a strongly T-dependent exponent δ(T). These features strongly support the proposal that, above Tc, the pair condensate survives to support significant London rigidity.