Role of atomic coordination on superconducting properties of boron-doped amorphous carbon

Abstract

We study the effect of atomic coordination (orbital hybridization) on superconducting properties of boron-doped amorphous carbon. The ratio of three-fold coordinated (sp 2 -hybridized) and fourfold coordinated (sp 3 -hybridized) atoms in the system is found to have an impact on their electronic, vibrational and superconducting properties. Our findings show that a high proportion of four-fold coordination in both carbon and boron atoms are important for realizing a high superconducting transition temperature.

High-temperature conventional superconductivity in the boron-carbon system: Material trends

“…Structures where bonds centered around B atoms are neither sp 2 nor sp 3 tend to exhibit a low T c , because the clustering of atoms around B tends to reduce the symmetry, depress the value of N(E F ), and hence T c . A similar behavior has been observed in amorphous Q carbon [45].…”

“…Several studies in literature have already predicted conventional superconductivity with sizable T c in the BC system for selected compositions and structural motifs [18,19,37,38]; a series of pioneering works by Moussa and Cohen analyzed T c trends in selected templates, using the rigid-band (RB) approximation for doping and the rigid-muffin-tin approximation for the ep coupling [39][40][41]. Moreover, recent experimental claims exist of a record T c of T c = 55 K (higher than in MgB 2 ) in B-doped (amorphous) Q carbon, which is consistent with an ep mechanism [42][43][44][45].…”

Heavy boron doping in superconducting carbon materials

“…Further low-frequency phonon modes below 200 cm −1 appears in bct C 4 (red solid lines in in bct C 4 is similar to that of amorphous carbon where large empty space also exists in its structure [20,21]. The high T c of 55 K in this structure suggests that perfect symmetry of crystal structure or perfect tetrahedra are not necessarily required to obtain such a high T c .…”

“…The recent finding of the high T c of 55 K in heavily boron-doped amorphous "Q-carbon" motivates further investigations of high T c in boron-doped carbon materials [19][20][21][22]. In particular, sp 3 -hybridized carbon materials should be of interest as Q-carbon is considered to be an sp 3 -rich material [23,24].…”

Structural Characterization of Graphite Analogue BCx Synthesized Under Various Conditions and Its Application to Ti Intercalation

“…This method generated Q-carbon with 27 atom % B substitution, exhibiting a high T c of 55 K. There is no independent experimental confirmation of superconducting Q-carbon by another group. However, theoretical calculations point out the possibility of high T c in B-doped carbon materials. − Thus, we attempted to substitute B with carbon materials.…”