High- Tc superconductivity in doped molecular superconductors of K4B8−xMxH32 (M = C, N) under high pressure

Abstract

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 K4B8H32 hydrides on the superconductivity at low pressures. As a result of various atoms substituting, we have found that metallic K4B _{8-x} M x H32 (M = C, N) hydrides are dynamically stable at 50 GPa, band structures and density of states (DOS) indicate that sizeable Tc correlates with a high B–H DOS at the Fermi level. With the increasing of B atoms in K4B _{8-x} M x H32 hydrides, the DOS 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 Tc from 19.04 to 77.07 K for KC2H8 and KB2H8 at 50 GPa. The NH4 unit in stable K4B7NH32 hydrides has weakened the EPC and led to low Tc value of 21.47 K. Our results suggest the light elements hydrides KB2H8 and K4B7CH32 could estimate high Tc values at 50 GPa, and the boron hydrides would be potential candidates to design or modulate hydrides superconductors with high Tc at moderate or ambient pressures.