Equilibrium superconducting properties of grain-aligned HgBa2Ca2Cu3O8+δ

The upper critical field Hc2 and other equilibrium properties of a magnetically aligned HgBa2Ca2Cu3O8+δ superconductor have been investigated. Experimental results for the reversible magnetization, both with Hc and Hab, are analyzed using the theoretical formalism of Hao et al. [Phys. Rev. B 43, 2844 (1991)] for type-II superconductors. Near Tc, the slopes dHc2/dT of the upper critical field are -1.6 T/K and -12.1 T/K for fields parallel and perpendicular to the c axis, respectively. These correspond to coherence lengths (extrapolated to T=0) of ξab(0)=15 and ξc=1.9 . This gives a lower bound on the superconductive anisotropy parameter γ=(mc/mab)1/28.