Magnetic Irreversibility of 31 K Electron Superconductor Nd1.85Ce0.15CuO3.93

黃建華(G. H. Hwang) ； 賀清華(T. H. Her) ； 古煥球(H. C. Ku)

《Chinese Journal of Physics》 28卷5期 (1990/10) Pp. 453-460

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並列摘要

Superconducting transition temperature Tc onset up to 31 K was reported for the oxygen-reduced electron superconductor Nd1.85Ce0.15CuO4-δ (δ=0.07(2)). Magnetic irreversibility line H*(T)=4.72(1-T/Tc)^5/3 T for applied filed up to 0.5 T and H*(T)=6.13(1-T/Tc)^7/4 T for applied filed up to 5T. The irreversibility line probably indicates the onset of vortex lattice melting, which is believed to be closely related to the quasi-two-dimensional nature of the system with small coherence length. Zero temperature lower critical field Hcl(0) of 17 G and upper critical field Hc2(0) of 23.5 T were extrapolated with derived long penetration depth λ(0) ≌ 6000 Ǻ and short coherence length ξ(0) ≌ 30 Ǻ. Msgnetic susceptibility measurement under applied magntic field of 20 G in the vortex state region (＞ Hcl) gives a diamagnetic fraction of -4πχ=0.14 at 5 K