Enhanced anisotropic nature ofHgBa2Ca3Cu4O10+δ

Abstract

Reversible magnetization of grain-aligned ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4}{\mathrm{O}}_{10+\mathrm{\ensuremath{\delta}}}$ with the external magnetic fields of 1 T $l~Hl~$ 5 T parallel to the $c$ axis has been measured. The application of the model of Hao et al. [Phys. Rev. Lett. 67, 2371 (1991); Phys. Rev. B 43, 2844 (1991)] to our data gives the anomalous temperature dependence of the Ginzburg-Landau parameter $\ensuremath{\kappa}(T)$, i.e., the increase of $\ensuremath{\kappa}$ with $T$, in the entire reversible region 81 K $l~Tl~$ 100 K. This implies that the thermal distortions of the vortices are not negligible even far below ${T}_{c}$ and thus the system is a highly anisotropic. This is supported by the two-dimensional scaling behavior of the magnetization in the critical region. From the model of Hao et al. we obtained various superconducting parameters such as the critical fields, the coherence length, and the penetration depth. In particular, the zero-temperature penetration depth ${\ensuremath{\lambda}}_{\mathrm{ab}}(0)$ is estimated to be 157 nm, which is the smallest of the Hg-based superconductors. We infer that this is due to the large hole density within the ${\mathrm{CuO}}_{2}$ plane.