Quantum Transport in Boron‐Doped Nanocrystalline Diamond

Abstract

Highly grained thin films of boron-doped diamond are grown by plasma-enhanced (PE)CVD. Diamond nucleation surface treatment is discussed, together with its relation to the morphology, topology, and phase composition of the layers. The influence of the random incorporation of boron atoms in a diamond lattice is described in terms of Mott's metal and the weak localization (WL) transport mechanism. Starting from these concepts and from the experimental transport data, we build up a simple original theory of the superconductivity in boron-doped diamond that is based on a spinflip pairing mechanism. We analyze an influence of the grain boundaries in nanocrystalline diamond (NCD) on superconductivity-related quantum transport phenomena, and show a decisive role of the weak links created by point contacts between grains.

Selected topics related to the transport and superconductivity in boron-doped diamond

“…The second approach, correctly describing most of the experimentally observed features, is 'correlated impurity band theory' of Baskaran [31]. The third variant of the theory accounting for superconductivity in B-NCD, which is due to the authors of this review, is based on the spin-flip-driven pairing of holes weakly localized in the vicinity of the Fermi level [11,32]. The simultaneous existence of different, more or less equally justified theories makes it obvious that the a-priori choice of a pairing mechanism followed, e.g.…”

“…Boron doped diamond (BDD), prepared either by high pressure high temperature technique (HPHT) [1,2], by plasma enhanced chemical vapour deposition (PECVD) [3][4][5] or by hot filament assisted CVD [6,7], is a unique material which provides the playground for various quantum transport phenomena, such as hopping, weak localization, ballistic transport, unconventional superconductivity and Josephson's effects [8][9][10][11][12]. The growth techniques mentioned above provide boron-doped diamond samples not essentially differing from one another.…”

Finite bias evolution of bosonic insulating phase and zero bias conductance in boron-doped diamond: A charge-Kondo effect

“…On the other hand 1D and 2D superconductors often demonstrate complex phase transitions that include an insulating phase with an anomalous resistivity peak in the vicinity of Tc [1]. It is well known that heavily boron doped diamond (HBDD) (films) exhibits a superconducting phase transition at low temperature with a transition width-critical temperature ratio (ΔT/Tc) that varies with grain size [2]. Further, it has recently been proposed that granular 3D heavily boron doped diamond (film) undergoes a metal-bosonic insulator (BI)-superconductor transition resulting in a giant anomalous resistivity peak (referred to as a bosonic insulator phase) in the vicinity of Tc [1].…”

“…Scanning electron microscopy images show that boron doped samples have a granular surface morphology with grain sizes that vary from 20-30 nm for sample B5 and 100 nm for sample B1 (See Fig. 1(a)) [2]. Resistance measurements were performed in a four-probe van der Pauw geometry.…”