Exposure of the MgB₂ A-plane via HPCVD Grown Tilted C-plane Films

Magnesium diboride (MgB₂) has shown promise as a potential single material topological superconductor with a superconducting transition temperature (T_c) around 40 K and topological bands observed on its A-plane (11-20) of single crystals (Zhou et al., Phys. Rev. B 100, 184511 (2019)). Only C-plane (0001) or small angle tilted MgB₂ thin films have been fabricated. While A-plane MgB₂ can be produced by cleaving bulk crystals, a method to deposit thin films is desired for combining with other materials for applications in quantum devices. Confirmed by x-ray diffraction (XRD), we demonstrate that large-scale (1-102) MgB₂ films can be grown via hybrid physical-chemical vapor deposition (HPCVD) on M-plane (1-100) sapphire. This tilts the C-plane 34° out-of-plane from the substrate, exposing the A-plane of MgB₂ and retains a high T_c of 38.8 K. Anisotropy of the critical field was verified using a four-probe resistance measurement with a maximum H_c2 parallel to the ab-axis. Details of structural, superconducting, and angular dependence of resistance and upper critical field properties will be presented.