Systematic study of novel BCS-type superconductors in ThCr₂Si₂-type crystals via ab-initio simulations

The ThCr₂Si₂-type compounds include exotic superconductors, such as iron-pnictide high-temperature superconductors, and BCS-type superconductors, such as iron-free pnictides. However, the superconducting transition temperatures (Tc) of many other compounds have not yet been investigated. In this study, we conducted a comprehensive investigation of BCS-type superconducting transition temperatures of the ThCr₂Si₂-type compounds using first-principles calculations. Our calculations successfully reproduced the previously reported Tc values, confirming SrPb₂Al₂ (Tc = 2.2 K) as a new superconductor.

Furthermore, to explore new superconductors, we focused on LaX₂Si₂, which has many reported B-site substitutions, and investigated the Tc of various substituted compounds. As a result, we discovered two new superconductors: LaCd₂Si₂ (Tc = 2.4 K) and LaZn₂Si₂ (Tc = 1.7 K), with LaCd₂Si₂ exhibiting the highest Tc in the LaX₂Si₂-type compounds.

Through our screening calculations, we found that the heavier the element at the B-site, the stronger the electron-phonon coupling becomes, and the larger the atomic radius, the more the crystal structure becomes quasi-two-dimensional, leading to two-dimensional Fermi surface. These results suggest that these factors play an important role in the emergence of superconductivity in ThCr₂Si₂-type compounds.

In the presentation, we will first explain the background of superconductivity research in ThCr₂Si₂-type compounds, then provide details of our computational methods and results, and finally connect these findings to the conclusions.