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

Abstract

We report on the pressure-driven superconductor-insulator transition in heavily boron-doped nanodiamond films. By systematically increasing the pressure, we suppress the Josephson coupling between the superconducting nanodiamond grains. The diminished intergrain coupling gives rise to an overall insulating state in the films, which is interpreted in the framework of a parallel-series circuit model to be the result of bosonic insulators with preserved localized intragrain superconducting order parameters. Our investigation opens up perspectives for the application of high pressure in research on quantum confinement and coherence. Our data unveil the percolative nature of the electrical transport in nanodiamond films, and highlight the essential role of grain boundaries in determining the electronic properties of this material.

Substrate mediated nitridation of niobium into superconducting Nb2N thin films for phase slip study

“…7(b). Usually for granular films, the two-step NM-SC transition as observed in R(T) data can be explained in terms of local and global superconductivity 17,18,32–34 . Here the differences in the grain size represent the inhomogeneous nature of the samples.…”

Anomalous Anisotropy in Superconducting Nanodiamond Films Induced by Crystallite Geometry

“…By decreasing the mean grain size, a systematic reduction of the coherence length was realized in a set of nanodiamond films [14]. When increasing the mean intergrain spacing or the applied pressure, a bosonic insulating state emerged in nanodiamond films as a result of suppressed intergrain Josephson coupling and localized intragrain superconducting order parameter [15][16][17][18].…”

Recent Progress of Nanodiamond Film in Controllable Fabrication and Field Emission Properties

“…For example, Su Q. et al synthesized the ND films via HFCVD and analyzed the effects of carbon concentration on the ND structure film [ 63 ]. As the carbon concentration ratio in the total gas increased, the ND grain size, the film roughness and the inter sp 3 carbon phase concentration decreased while the sp 2 carbon phase increased in nano-diamond films in Figure 4 a. Additionally, a heavily boron (B)-doped ND thin films was also fabricated by the HFCVD, which can be converted from a superconductor to an insulation by the pressure driven as shown in the SEM/cross section STEM image and the characteristic EELS spectra recorded from the intragrain and intergrain regions of the heavily boron-doped nanodiamond films ( Figure 4 b), which was attributed to the suppression of the Josephson intergrain coupling between the superconducting nanodiamond grains [ 74 ]. So far, the HFCVD technology is still a popular approach to fabricate the ND films due to the relatively low equipment cost and simple process.…”

“…The growth parameters using CVD with different energy source are summarized in Table 1 . It can be concluded that the obtained ND films from various CVD method are normally grown in a H 2 -rich, carbon-containing gas-lean mixture atmosphere under growth substrate temperature from 250 °C to 1200 °C [ 59 , 62 , 64 , 69 , 70 , 71 , 72 , 73 , 74 , 75 ]. Presumably the higher ratio of CH 4 in H 2 , the more non-diamond carbon incorporation quantity, and the smaller grain size of ND particle in ND film.…”

“… The synthesized ND film via hot filament CVD. ( a ) The SEM images of the synthesized ND films under different carbon concentration ratio [ 63 ], ( b ) the SEM image ( a’ ), cross section STEM image ( b’ ), STEM-EELS image of boron (in green) and carbon (in red) distributions in the white dashed window of STEM image ( c’ ), and the characteristic EELS spectra ( d’ ) recorded from the intragrain and intergrain regions of the heavily boron-doped nanodiamond films [ 74 ], ( c ) a nanocrystalline diamond multilayer system including two conductive nanocrystal-line diamond layers and one non-conductive nanocrystalline diamond [ 75 ]. …”