Irradiation-Induced Modification of the Superconducting Properties of Heavily-Boron-Doped Diamond

Abstract

Diamond, a wide band-gap semiconductor, can be engineered to exhibit superconductivity when doped heavily with boron. The phenomena has been demonstrated in samples grown by chemical vapour deposition where the boron concentration exceeds the critical concentration for the metal-to-insulator transition of nMIT 4 × 10 20 /cm 3 . While the threshold carrier concentration for superconductivity is generally well established in the literature, it is unclear how well correlated higher critical temperatures are with increased boron concentration. Previous studies have generally compared several samples grown under different plasma conditions, or on substrates having different crystallographic orientations, in order to vary the incorporation of boron into the lattice. Here, we present a study of a single sample with unchanging boron concentration, and instead modify the charge carrier concentration by introducing compensating defects via high energy ion irradiation. Superconductivity is completely suppressed when the number of defects is sufficient to compensate the hole concentration to below threshold. Furthermore, we show it is possible to recover the superconductivity by annealing the sample in vacuum to remove the compensating defects. arXiv:1809.01800v1 [cond-mat.supr-con]

Anomalous Anisotropy in Superconducting Nanodiamond Films Induced by Crystallite Geometry

“…Superconducting diamond in the form of a polycrystalline film offers additional opportunities for the investigation of its superconducting properties as a function of parameters other than the boron-doping level. Suppression and recovery of the superconductivity in a heavily boron-doped diamond film were previously achieved by ion irradiation and annealing, respectively [13]. By decreasing the mean grain size, a systematic reduction of the coherence length was realized in a set of nanodiamond films [14].…”

Weak Electron Irradiation Suppresses the Anomalous Magnetization of N‐Doped Diamond Crystals

“…A recently published study on the influence of ion irradiation on the SC of heavily B-doped diamond samples, showed that SC is suppressed after He-ion irradiation of 5 Â 10 16 at 1 MeV producing a vacancy concentration of ≃ 3 Â 10 21 cm À3 (% 2%). [17] This apparent complete suppression of SC after irradiation was experimentally observed by electrical resistance measurements. Therefore, we may further ask, if the nominal concentration of produced vacancies by the irradiation that affects the magnetic properties is also of the order of the C-center concentration.…”

“…[12][13][14][15] The granular nature of the SC phase and localized disorder may play an important role as recently reported experimental facts indicate, namely: a) not always there is a clear correlation between the B-concentration threshold for the metal-insulator transition and the one for SC, [16] and b) there is no simple dependence between the free-carrier concentration and the critical temperature characterized by transport measurements. [17] Another open issue in the SC puzzle of doped diamond is the fact that implanting boron into diamond via irradiation does not trigger SC at least above 2 K. [18] It has been argued that this irradiation process does not trigger SC because of the produced defects that remained in the diamond lattice after ion irradiation. However, this is not at all clear because the sample was heated to 900 C during irradiation and afterward annealed at 1700 C in vacuum, [18] see also similar results in the studies by Willems van Beveren et al and Tsubouchi et al [19][20][21] It might be that the absence of SC in the irradiated samples after high temperature annealing is related to the absence of certain defects and not other way around.…”

“…It has been argued that vacancies change the effective carrier density compensating the boron acceptors and therefore suppressing SC. [17] 1.2. Defect-Induced Phenomena and the Unconventional Magnetization Observed in Nitrogen-Doped Diamond Crystals According to recent studies, the reported SC in B-doped diamond appears to be more complicated because not only the boron concentration matters but also some kind of disorder or even magnetic order may play a role.…”

Superconductor-insulator transition driven by pressure-tuned intergrain coupling in nanodiamond films

“…Our picture, based on pressure-enhanced granular disorder, does not consider the existence of an intermediate metallic but normal phase, although such a phase has been reported for a set of diamond films with different boron concentrations and a superconducting diamond film irradiated at different fluences [13,32]. In contrast to our methodology, the techniques used in these two studies exert a direct and vital influence on the process of Cooper pairing itself.…”