Magnetically coupled pancake vortex molecules in HgBa2Can-1CunOy (n≥6)

As recently shown, HgBa2Can-1CunOy (n >= 6) cuprate superconductors have a critical temperature of about 100 K independent of n. This remarkable property can be explained by the very imbalanced distribution of carriers among the inequivalent CuO2 planes in the unit cell. We discovered that these materials also have a common vortex melting line that resembles the theoretical melting lines of magnetically coupled pancake vortices. We suggest that there are two types of pancake pairs situated in the superconducting CuO2 outer planes: those separated by the thin charge reservoir layer are strongly (Josephson) coupled, while those separated by the thick block of (n-2) CuO2 nonsuperconducting inner planes are weakly (magnetically) coupled, forming magnetically coupled pancake vortex molecules.