Supercurrents in HgBa2CaCu2O6+delta and TlBa2CaCu2O7 epitaxial thin films

The availability of high-quality epitaxial thin films of HgBa2CaCu2O6+delta (Hg-1212) and TlBa2CaCu2O7 (Tl-1212) with high critical current densities (J(c)) has made it possible to examine and compare the J(c) of these specie s. Results reveal that the J(c) of 1212 species have very similar temperatu re behavior at low fields, strongly suggesting that the 30 K shift in criti cal temperature (T-c) induced by the exchange of Hg and Tl in the 1212 stru cture is due largely to a change in charge carrier density and/or electroni c band structure. (C) 1999 American Institute of Physics. [S0003-6951(99)02 825-9].