First-principles study of the superconductivity of MoB2 under low pressure and its evolution under high pressure

Abstract

Ever since it was found that MoB2 holds the second-highest superconductive transition temperature (Tc, 32 K) amongst all known diborides, the argument on the donation of its two phases, the high-pressure α−MoB2 phase (hexagonal, P6/mmm) and the low-pressure β-MoB2 (rhombohedral, R−3m) has never stopped, because the phase-transition pressure is approximately 50 GPa higher than the pressure that superconductivity takes place. We simulated the phase transition and the possible superconductive properties of the two phases, and found that the ordered stacking arrangement ensures the p-d hybridization near the Fermi level and induces significant electron-phonon coupling, which actually influences the superconductivity. Therefore, the α−MoB2 is the only phase that could be a superconductor. With our simulation, instead of further increasing, the Tc of MoB2 would decrease slowly after reaching the maximum with a d Tc/dp of −0.014 K/GPa, primarily due to the expected decrease and saturation of the electron-phonon coupling constant (λ) mainly contributed by Mo, along with the higher-frequency moments provided by B atoms under higher pressure. Therefore, in a certain transition-metal boride, it is not only the relatively high-frequency moments induced by B atoms, but also the stacking structure of them drives the electrons around transition-metal core in good symmetry and strengthens electron-phonon coupling, which leads to good superconductivity. Therefore, to manipulate boron-layer stacking arrangements might be an important angle to design and develop cutting-edge superconducting borides.

Source-reported materials — not catalogue approval

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