Vortex dynamics in Hg-based multi- and super-multi-layered cuprates

Abstract

Hg-based multi- and super-multi-layered cuprates HgBa2Can-1CunOy (Hg:12(n-1)n) (n⩾4) are composed of the charge reservoir layer (CRL) HgBa2Ox, and of CuO2 planes: outer planes (OP) with pyramidal oxygen coordination and inner planes (IP) with square oxygen coordination, with different charge distribution. This fact gives rise to very interesting phenomena, like coexistence of superconductivity (SC) in OPs with antiferromagnetism (AF) in IPs in Hg:1245. The dependence of Tc on the number n of CuO2 planes is also interesting: for n increasing from 4 to 5 and to 6, Tc decrease from 125 to 108 and then to about 103 K; further increase in n keeps Tc constant at about 103 K. In Hg:1245 we show that the AF ordering at TN of 60 K has no influence on vortex dynamics, and there is a quite robust c-axis supercurrent. Vortex melting lines of various samples showed that Hg-based multi-layered cuprates (n = 4, 5) behaves in the usual way (increasing n resulted in decrease of Josephson coupling (JC) and a less sharp melting line) and are well described by the usual anisotropic GL-based theory. Samples with n ⩾ 6 have all the same melting line, suggesting that, in this case, the short-range JC becomes much less important than the long-range magnetic coupling (MC). However, since the JC between two pancakes in OPs of adjacent unit cells (pancakes separated by the thin CRL) is large, we suggest that the vortex matter in Hg-based super-multi-layered cuprates is composed of magnetically-coupled pancake-vortex-molecules.