Comparative transport studies of '1212' superconductors

Abstract

The purpose of this study is to ascertain the nature of the 30-K shift in the critical temperature (T_c) in exchanging the Tl cation in TlBa₂CaCu₂O_6+δ (Tl-1212, T_c ~ 90 K) with the Hg cation to produce HgBa₂CaCu₂O_6+δ (Hg-1212, T_c ~ 120 K). This rare availability of high quality samples of both '1212' species makes this study possible, and could shed new light on the still-unexplained mechanism of high-temperature superconductivity. Since the Hg-1212 films were fabricated from Tl-1212 by replacing Tl cations by Hg cations the superconducting '1212' layered structured is preserved under this cation exchange; therefore the T_c shift is not due to the anisotropic layered structure prevalent in high-temperature superconductors, but more likely due to differences in the electronic structure and charge carrier density. It will be shown that the T_c shift is due primarily to a shift in charge carrier density.