Metal-Bosonic Insulator-Superconductor Transition in Boron-Doped Granular Diamond

In a variety of superconductors, mostly in two-dimensional (2D) and one-dimensional (1D) systems, the resistive superconducting transition R(T) demonstrates in many cases an anomalous narrow R(T) peak just preceding the onset of the superconducting state R = 0 at T-c. The amplitude of this R(T) peak in 1D and 2D systems ranges from a few up to several hundred percent. In three-dimensional (3D) systems, however, the R(T) peak close to T-c is rarely observed, and it reaches only a few percent in amplitude. Here we report on the observation of a giant (similar to 1600%) and very narrow (similar to 1 K) resistance peak preceding the onset of superconductivity in heavily boron-doped diamond. This anomalous R(T) peak in a 3D system is interpreted in the framework of an empirical model based on the metal-bosonic insulator-superconductor transitions induced by a granularity-correlated disorder in heavily doped diamond. DOI: 10.1103/PhysRevLett.110.077001