Anisotropic Magneto-transport in Homoepitaxial Superconducting Boron Doped Diamond Thin Films

Two decades since its discovery [Nature 428, 542–545 (2004)], superconductivity in heavily boron doped diamond (HBDD) presents unresolved fundamental questions regarding its origins. Our electrical magnetotransport measurements of homoepitaxial single crystal HBDD films bear the hallmarks of granular superconductivity which is expected to be isotropic. However, the dependence of electrical resistivity on temperature, magnetic field vector, and current density reveals a surprising three-phase anisotropy, accompanied by a spontaneous transverse voltage (Hall anomaly) at the metal-superconductor phase transition. These observations indicate the emergence of a magnetic and electric field-tunable intrinsic order in an otherwise isotropic single crystal HBDD film, suggesting that its granular superconductivity might have electronic origins. Understanding the source of this anisotropic granularity can provide new perspectives into the mechanism of superconductivity in covalent metals and lead us closer to the theoretically predicted enhanced superconducting transition temperature [J. Phys. Soc. Jpn. 76, 014711 (2007)] in ``disorder-free'' HBDD crystals.