Chiral-Structured Superconductors TrX4 (Tr = Rh, Ir; X = Ge, Si): A Platform for Mixed-Parity Pairing and Topological States.

Chiral-structured superconductors, with simultaneous broken mirror and inversion symmetries, promote unconventional superconductivity through parity-mixing mechanisms. Yet a few bulk chiral-structured superconductors are known, partly due to the difficulty in directly determining their atomic-scale chirality. Here, we report three chiral-structured superconductors, RhGe4, IrGe4, and IrSi4, synthesized under high pressure, with Tc values of ∼2.6, 1.1, and 2.5 K, respectively. Using atomic-resolution Cs-corrected scanning transmission electron microscopy (STEM) combined with X-ray diffraction characterizations, we directly confirm their chiral structure (space group P3121). This real-space imaging approach overcomes ambiguities in traditional diffraction-based methods. These materials exhibit type-II superconductivity, and the enhancement of spin-orbit coupling (SOC) leads to the emergence of mixed-parity pairing. Calculations also reveal symmetry-protected Weyl points near the Fermi level, which is robust against the SOC. Our work not only expands the family of chiral-structured superconductors but also demonstrates the indispensable role of STEM in directly determining chiral crystal structures. These materials thus offer a clean platform to explore the interplay among structural chirality, spin-orbit coupling, mixed-parity superconductivity, and topological quantum phenomena.