Spin-Valley Locking and Pure Spin-Triplet Superconductivity in Noncollinear Antiferromagnets Proximitized to Conventional Superconductors

Abstract: Unconventional antiferromagnets with spin-split bands, such as noncollinear magnets and the recently discovered altermagnets, serve as new constituents to explore unconventional superconductivity. Here, we unveil a new type and previously unappreciated nature of spin-valley locking in noncollinear antiferromagnets and exploit this texture to achieve pure spin-triplet superconductivity. Using chiral antiferromagnetic kagome lattices (e.g., Mn$_3$Ge and Mn$_3$Ga) coupled to conventional $s$-wave superconductors as prototypical examples, we demonstrate that the antiferromagnetic chirality strongly favors spin-triplet pairing via superconducting proximity effect, while suppressing spin-singlet pairing in the antiferromagnets away from the interfaces. Crucially, such a long-sought spin-triplet superconducting state is established without invoking the prevailing mechanism of spin-orbit coupling or net magnetization. Furthermore, the spin-triplet supercurrent is resilient to both in-plane and out-of-plane Zeeman fields, which exhibits distinct superiority to Ising superconductivity, serving as a compelling experimental signature of the triplet pairing and spin-valley-locked texture.