Th₂Mo₂Ir₂Si₄C: An Intergrown Superconductor by Structure Design

Exploration of new superconductors in multicomponent complex systems remains challenging. Among complex superconductors, those containing distinct superconducting layers are quite rare. In this work, based on the block-layer model together with formation energy calculations, we have designed and successfully synthesized a quinary intermetallic compound, Th₂Mo₂Ir₂Si₄C. The new material crystallizes in an intergrowth structure with an alternate stacking of superconducting ThMo₂Si₂C and ThIr₂Si₂ block layers along the crystallographic c axis. The interblock-layer interaction is dominated by the Si-Ir bonding, which results in a relatively shorter interlayer distance and a stronger coupling between [Mo₂Si₂C] and fluorite-type [Si₂Ir₂] layers. Enhanced superconductivity, with a superconducting transition temperature of T_c = 3.4 K and a zero-temperature upper critical field of H_c2(0) = 9.5 kOe, is revealed by measurements of electrical resistivity, magnetic susceptibility, and specific heat. The strategy of the block-layer design demonstrated here can be extended to other intergrowth systems with various functional motifs.