Intrinsic granularity in nanocrystalline boron-doped diamond films measured by scanning tunneling microscopy

Abstract

We report on low-temperature scanning tunneling microscopy/spectroscopy experiments performed on superconducting boron-doped nanocrystalline diamond ͑NCD͒ thin films prepared by chemical-vapor deposition methods. The most representative sample reveals the observed superconducting gap ͑⌬͒ highly modulated over a length scale on the order of ϳ30 nm, which is much shorter than the typical diamond grain size. The sample local and macroscopic behavior favors for the ⌬ modulation as being an intrinsic property of the NCD granules. On the other hand, ⌬ shows its temperature dependence ͓⌬͑T͔͒ consistent with the results obtained by Fominov and Feigel'man ͓Phys. Rev. B 63, 094518 ͑2001͔͒, who studied theoretically the behavior of the superconducting gap of a BCS superconductor in contact with a normal layer by solving the one-dimensional Usadel equations on the superconducting side of the superconducting to normal interface.

Superconducting Density of States in B-Doped Diamond

“…2, the superconducting gap in the density of states is gradually suppressed with increase of temperature and the estimated superconducting critical temperature T c = 7 ± 0.5 K. Such measurements were performed at numerous locations across the sample surface, yielding identical results within experimental error. We did not observe any spatial variation of SDOS as reported in previous studies of polycrystalline boron doped diamond [11][12][13][14]. Notably, the value of the differential conductance inside the superconducting gap is equal to zero (see Fig.…”

“…3). This is in steep contrast with previous studies on polycrystalline samples [11][12][13][14]. To our knowledge, such homogeneous hard gap was observed only in the case of a single crystal [15].…”

Flux pinning and improved critical current density in superconducting boron doped diamond films

“…Among these works, mention can be made of the work by Bustarret et al [11], which showed the dependence of T c on the doping level in high quality single crystalline diamond and Klein et al [12] studied boron doping induced IMT where the dependence of T c on boron concentration (n B ) in granular BDD was demonstrated. The work by Willem et al [13] and Zhang et al [14], showed the microscopically inhomogeneous nature of superconductivity in BDD. Importance of spin ordering and disorder have been highlighted by Zhang et al, revealing ferromagnetism [15] and anomalous resistance peak [16,17] in superconducting diamond.…”

Spatially correlated microstructure and superconductivity in polycrystalline boron-doped diamond

“…6 In such systems, disorder sits either at the atomic scale, in which case electronic excitations can become localized so that superconductivity vanishes 7 or at a larger scale, for instance, that of a granular structure, in which case the two competing mechanisms are the Coulomb blockade and the superconducting proximity effect. 8,9 Nevertheless, recent studies of polycrystalline diamond films 10,11 did not provide a clear picture on the coexistence between superconductivity and disorder in these films.…”