Superconductivity in the Locally Noncentrosymmetric Th ₂ Mo ₂ Rh ₂ Si ₄ C by Rational Design

Locally noncentrosymmetric (LNC) superconductors with broken local inversion symmetry can exhibit exotic properties due to antisymmetric spin-orbit coupling (SOC). A promising strategy to construct LNC superconductors is to incorporate LNC blocks into superconducting lattices. Herein, a complex LNC superconductor, Th₂Mo₂Rh₂Si₄C, was designed and successfully synthesized. This compound adopts a unique 22241* structure, in which the superconducting [Mo₂Si₂C] block loses its out-of-plane mirror symmetry due to being sandwiched between antifluorite-type [Rh₂Si₂] and fluorite-type [Si₂Rh₂] layers. Physical property measurements indicate the title compound exhibits bulk superconductivity with a remarkably enhanced upper critical field μ₀<i>H</i>_c2(0) of 1.39 T, five times higher than that of the constituent ThMo₂Si₂C, albeit with a similar transition temperature <i>T</i>_c = 2.1 K. First-principles calculations further reveal a Rashba-type SOC due to the lack of local inversion symmetry, which results in multiple gapped band crossings and significant band splitting near the Fermi level. This work provides a new material platform to study the interplay between superconductivity and Rashba-type SOC and lays a rational path for the exploration of LNC superconductors.