High- T c superconductivity in doped molecular superconductors of K 4 B 8-x M x H 32 (M = C, N) under high pressure.

Stabilized and metallic light elements hydrides have provided a potential route to achieve the goal of room-temperature superconductors at moderate or ambient pressures. Here, we have performed systematic DFT theoretical calculations to examine the effects of different light elements C and N atoms doped in cubic K 4 B 8 H 32 hydrides on the superconductivity at low pressures. As a result of various atoms substituting, we have found that metallic K 4 B 8-x M x H 32 (M = C, N) hydrides are dynamically stable at 50 GPa, band structures and density of states indicate that sizeable T c correlates with a high B-H density of states at the Fermi level. With the increasing of B atoms in K 4 B 8-x M x H 32 hydrides, the density of states values at Fermi level have been improved due to the delocalized electrons in B-H bonds, which result in strong electron-phonon coupling (EPC) interaction and increase the T c from 19.04 to 77.07 K for KC 2 H 8 and KB 2 H 8 at 50 GPa. The NH 4 unit in stable K 4 B 7 NH 32 hydrides has weakened the EPC and led to low Tc value of 21.47 K. Our results suggest the light elements hydrides KB 2 H 8 and K 4 B 7 CH 32 could estimate high T c values at 50 GPa, and the boron hydrides would be potential candidates to design or modulate hydrides superconductors with high T c at moderate or ambient pressures.