New carbon allotropes and their B-doped phases as candidate for Q-carbon materials with magnetic and superconducting properties

Recent experimental studies have indicated that quenched sp2-sp3 hybridized carbon materials (Q-carbon) exhibit ferromagnetism with relatively high Curie temperature [1] and even superconductivity with high critical temperature (Tc) in their B-doped phases [2]. However, local structure of Q-carbon has not been clarified yet. Therefore, further theoretical studies are indispensable. Here we propose a new carbon allotrope with similar concentration of sp2-sp3 hybridized atoms to Q-carbon. We study their electronic properties including related allotropes previously proposed so far based on the density functional theory (DFT). Only the carbon allotrope we newly propose is found to exhibit magnetic moment which is closer to experimental value [1]. We further estimate Tc of the B-doped allotropes using the McMillan formula and the density functional perturbation theory (DFPT). The estimated Tc value for carbon allotrope with an appropriate B concentration also agrees well with the experimental value [2], indicating that our new allotrope and its B-doped phases are good candidate for Q-carbon.



[1] J. Narayan and A. Bhaumik, J. Appl. Phys. 118, 215303 (2015).

[2] A.Bhaumik, R. Sachan, S. Gupta, and J. Narayan, ACS Nano 11, 6351 (2017).