Superconductivity of 132 K in HgBa₂Ca₂Cu₃O_8+δthin films fabricated using a cation exchange method

Abstract

A cation exchange method was applied to convert epitaxial TlBa 2 Ca 2 Cu 3 O 8 (Tl-1223) and Tl 2 Ba 2 Ca 2 Cu 3 O 10 (Tl-2223) precursor superconducting thin films to epitaxial HgBa 2 Ca 2 Cu 3 O 8+δ (Hg-1223) films on LaAlO 3 (001) substrates. While the conversion of Tl-1223 to Hg-1223 was partially successful, high-quality epitaxial Hg-1223 films were obtained from Tl-2223 precursor films. A critical transition temperature T c of up to 132 K has been demonstrated for the Hg-1223 films, which is close to the optimal value of 135 K reported on Hg-1223 bulk samples. The critical current density J c of the Hg-1223 films was up to 0.25 MA cm −2 at 77 K and self-field. This work represents the first success in achieving the highest-T c epitaxial Hg-1223 films using the cation exchange method, which are promising candidates for device applications with operational temperatures significantly above the temperature of liquid nitrogen.

Tl2Ba2CaCu2O8 bicrystal Josephson junctions operated close to 100 K

“…As a result, some non-superconducting phases may occur during the crystallization of thin films, which is one of the difficulties in the fabrication process. Comparing with the Hg-based JJs, Tl-based JJs are much easier to be prepared because the fabrication process of Tl-based films is less complicated than Hg-based films [34,35], especially Tl-2212 films can be easily achieved in large-area [36]. However, close to T c , thermally activated phase slippage (TAPS) [37] can disrupt the coupling of the order parameter of the two superconductors forming a Josephson junction.…”