Electrical transport and Seebeck measurements in highly disordered channels buried in diamond

Ion implantation enables the creation of conductive channels buried beneath the surface of diamond, with their depth, thickness, and microstructure being controllable through careful selection of implantation and annealing parameters. We investigate the low-temperature dependence of electrical conductivity and the Seebeck coefficient in these channels, which consist of an intricate network of various sp${}^n$ carbon configurations with different topologies and geometries at the nanometer scale. As the annealing temperature increases, we observe the existence of two distinct electronic transport regimes, characterized by a change in the curvature of the temperature-dependent conductivity and a sign change in the Seebeck coefficient, differing by several orders of magnitude between the two regimes. We show that these temperature-dependent behaviors are remarkably well captured by a hopping-based electronic transport model, where the overall conductivity results from a set of non-interacting percolation paths, and that the two regimes are associated with two distinct statistics that describe the distribution of the percolation paths in the system.