Slow Electron–Phonon Cooling in Superconducting Diamond Films

Titova, N.; Кардакова, А. И.; Tovpeko, N. A.; Ryabchun, S. A.; Mandal, Soumen; Morozov, D.; Klemencic, Georgina M.; Giblin, Sean; Williams, Oliver A.; Gol’tsman, G.; Klapwijk, T. M.

doi:10.1109/tasc.2016.2638199

Cited by 4 publications

(1 citation statement)

References 21 publications

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“…The intragrain diffusion constant, D, is calculated from the gradient of this plot as 11.5±5.7 cm 2 /s. The bulk diffusion constant for a BNCD film grown under the same conditions was recently measured to be 0.6 cm 2 /s [36]; if we replace the Thouless energy with the tunnelling energy, we obtain the effective intergrain diffusion constant defined as D eff = a 2 Γ/h [4] which we find to be 0.54±0.36 cm 2 /s, showing that this method of extracting physical parameters is consistent with other approaches.…”

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Fluctuation spectroscopy as a probe of granular superconducting diamond films

Klemencic

Fellows

Werrell

et al. 2017

Phys. Rev. Materials

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We present resistance versus temperature data for a series of boron-doped nanocrystalline diamond films whose grain size is varied by changing the film thickness. Upon extracting the fluctuation conductivity near to the critical temperature we observe three distinct scaling regions -3D intragrain, quasi-0D, and 3D intergrain -in confirmation of the prediction of Lerner, Varlamov and Vinokur. The location of the dimensional crossovers between these scaling regions allows us to determine the tunnelling energy and the Thouless energy for each film. This is a demonstration of the use of fluctuation spectroscopy to determine the properties of a superconducting granular system. Tunable granular materials offer rich physical systems with which to study the interplay between electron correlations and the mesoscopic effects of disorder. The occurrence of the metal-insulator and superconductorinsulator transitions appear to be strongly linked to granularity, be it structural or pertaining to variations of the order parameter [1][2][3]. There are also clear theoretical predictions for the signature of granularity in the transport properties of disordered superconductors close to the superconducting transition [4][5][6][7]. Boron doped nanocrystalline diamond (BNCD) provides a suitable tuneable material in which to explore these theoretical predictions. Superconductivity was first observed in high-pressure, high-temperature fabricated boron doped diamond in 2004 [8]. The phenomenon was quickly demonstrated in both single-crystalline [9] and polycrystalline [10] diamond synthesised by chemical vapour deposition (CVD). While superconductivity in doped semiconductor materials [11,12] is an active area of research, and although nanocrystalline diamond retains many of the desirable mechanical properties of single-crystalline material [13], a sometimes overlooked property in the study of superconductivity in polycrystalline boron-doped diamond is the physical granularity itself.A clear experimental signature of superconducting granular systems, as pointed out by Lerner, Varlamov and Vinokur [5] (henceforth referred to as LVV), is that there are three distinct temperature regimes in the vicinity of the critical temperature (T c ), distinguished by the magnitude of the temperature-dependent GinzburgLandau coherence length. At temperatures immediately above T c , short-lived Cooper pairs act as charge carriers, modifying the conductivity. The principal modification close to T c is the Aslamazov-Larkin pair contribution to the conductivity -the so-called paraconductivity [14]. When the coherence length is much larger than the typical grain size, the granularity is not seen by a Cooper pair and the system behaves as a 3D superconductor with paraconductivity taking the well-known form ∝ −1/2 , where = (T − T c )/T c is the reduced temperature. When the coherence length is comparable to the typical grain size, each grain acts as its own 0D superconductor for which the paraconductivity is expected to be ∝ −2 . However, in addition, the...

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