Fluctuation spectroscopy in granular superconductors with application to boron-doped nanocrystalline diamond

D. T. S. Perkins; G. M. Klemencic; J. M. Fellows; R. A. Smith

doi:10.1103/PhysRevB.104.094513

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Fluctuation spectroscopy in granular superconductors with application to boron-doped nanocrystalline diamond

D. T. S. Perkins, G. M. Klemencic, J. M. Fellows, R. A. Smith

DOI 10.1103/PhysRevB.104.094513 · Physical Review B

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Abstract

We perform a detailed calculation of the various contributions to the fluctuation conductivity of a granular metal close to its superconducting transition. We find three distinct regions of power law behavior in reduced temperature, η=(T−Tc)/Tc, with crossovers at Γ/Tc and ETh/Tc, where Γ is the electron tunneling rate, and ETh is the Thouless energy of a grain. The calculation includes both intergrain and intragrain degrees of freedom. This complete theory of the fluctuation region in granular superconductors is then compared to experimental results from boron-doped nanocrystalline diamond, using the assumption of a constant phase breaking rate τϕ−1. We find a semiquantitative agreement between the theoretical and experimental results only in the case of large phase breaking. We argue that there may be a phase breaking mechanism in granular metals worthy of further experimental and theoretical investigation.