Europhys. Lett.
Volume 72, Number 3, November 2005
Page(s) 451 - 457
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 05 October 2005
Europhys. Lett., 72 (3), pp. 451-457 (2005)
DOI: 10.1209/epl/i2005-10254-4

Strongly nonlinear magnetization above Tc in $\chem{Bi_2Sr_2CaCu_2O_{8+\delta}}$

Lu Li1, Yayu Wang1, M. J. Naughton2, S. Ono3, Yoichi Ando3 and N. P. Ong1

1  Department of Physics, Princeton University - NJ 08544, USA
2  Department of Physics, Boston College - Chestnut Hill, MA 02467, USA
3  Central Research Institute of Electric Power Industry Komae, Tokyo 201-8511, Japan

received 26 July 2005; accepted 12 September 2005
published online 5 October 2005

Using high-resolution magnetometry we have investigated in detail the magnetization M above the critical temperature Tc in $\chem{Bi_2Sr_2CaCu_2O_8}$. 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 $T\rightarrow T_c$, the susceptibility $\chi(T,H)$ diverges to very large values ( $\chi \rightarrow -1$) if measured in weak H. In addition, M(H) displays an anomalous non-analytic form $M\sim H^{1/\delta}$ in weak fields with a strongly T-dependent exponent $\delta(T)$. These features strongly support the proposal that, above Tc, the pair condensate survives to support significant London rigidity.

74.72.-h - Cuprate superconductors (high-$T_{\rm c}$ and insulating parent compounds).
74.25.Ha - Magnetic properties of superconductors.
74.25.Dw - Superconductivity phase diagrams.

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