Pt-Bi Antibonding Interaction: The Key Factor for Superconductivity in Monoclinic BaPt2Bi2

In the search for superconductivity in BaAu2Sb2-type monoclinic structure, we have successfully synthesized a new compound BaPt2Bi2, which crystallizes in the space group P21/m (S.G. 11; Pearson symbol mP10) according to a combination of powder and single crystal X-ray diffraction and scanning electron microscopy. Sharp electrical resistivity drop and large diamagnetic magnetization below 2.0 K indicates it owns the superconducting ground state. This makes BaPt2Bi2 the first reported superconductor in mono-clinic BaAu2Sb2-type structure, a previously unappreciated structure for superconductivity. First-principles calculations considering the spin-orbit coupling indicate that Pt-Bi anti-bonding interaction plays a critical role in inducing superconductivity.