Observation of Surface Superconductivity in a 3D Dirac Material

Superconductivity becomes more interesting when it encounters dimensional constraint or topology because it is of importance for exploring exotic quantum phenomena or developing superconducting electronics. Here, the coexistence of naturally formed surface superconducting state and 3D topological Dirac state in single crystals of BaMg2Bi2 is reported. The electronic structure obtained from the first-principles calculations demonstrates that BaMg2Bi2 is an ideal Dirac material, in which the Dirac point is very close to the Fermi level and no other energy band crosses the Fermi level. Superconductivity up to 4.77--5.17 K can be observed under ambient pressure in the measurements of resistivity. The anisotropic upper critical field and angle dependent magnetoresistance reveals the 2D characteristic of superconductivity, indicating that superconductivity occurs on the surface of the sample and is absent in the bulk state. The study not only provides BaMg2Bi2 as a suitable platform to study the interplay between superconductivity and topological Dirac state but also indicates that MgBi-based materials may be a promising system for exploring new superconductors.