A team of materials researchers at the University of Tokyo, headed by Masafumi Horio, have taken a dramatic step towards explaining the inner workings of high-temperature cuprate superconductors. Their latest work looks at the trilayer cuprate Hg1223, which has recently shown superconductivity up to a remarkable 134 Kelvin. This finding raises the quality of Hg1223 to one of the best-performing superconductors at ambient pressure. It even beats Bi2223, the most famous trilayer cuprate, which has a record superconductivity of 110 Kelvin (-163°C).
Horio and his team used Angle-Resolved Photoemission Spectroscopy (ARPES) to investigate the electronic structure of the substituted cuprate (Hg,Re)1223. Their research led to groundbreaking discoveries regarding this formidable yet versatile material. Researchers synthesized this variant of the compound by substituting some mercury atoms with rhenium (Re) atoms. This substitution is done to help stabilize the crystal structure. From these results they inferred that the superconducting gap of the inner CuO2 layer in (Hg,Re)1223 equals 63 meV. This value is about 10% larger than the corresponding 62 meV measured for Bi2223.
What is special about the chemistry of these trilayer cuprates is their structure, which includes three layers of CuO2 planes. Due to the relative ease of synthesizing Bi2223 over Hg1223, researchers have been able to much more easily compare their physical properties to one another. For Bi2223, the inner CuO2 layer exhibits a superconducting gap considerably larger than that of the outer layers. Notably, it is 62 meV for the inner layer while only reaching 43 meV for the outer layers. In sharp contrast, the outer layers of (Hg,Re)1223 show a large superconducting gap of 57 meV.
For example, Horio’s findings underscore the importance of robust pairing in the inner plane for trilayer cuprates. Evidence suggests that increased outer plane pairing energy is essential for achieving highest critical temperature at ambient pressure.
“While strong pairing in the [inner plane] has been highlighted as the key element of trilayer cuprates,” – M. Horio et al.
“The present results suggest that the enhanced pairing energy in the [outer plane] is essential for the highest Tc [critical temperature] at ambient pressure realized in the Hg-based trilayer cuprate.” – M. Horio et al.
Such insights can open new avenues for future research including cuprate superconductors. They might pave the way for creating new sorts of materials that would superconduct at even warmer temperatures. The study sheds light on the contradictory nature of these toxic substances. It further highlights the necessity of understanding their complex architectures and electronic correlations.