High-temperature superconductivity in clathrate thorium-doped hexahydrides A1−xThxH6 (

The discovery of high-temperature superconductivity in hydrides provides a promising route to achieve the goal of room-temperature superconductivity, but the ultrahigh pressure required to be synthesized severely limits their application. The next challenge is to find novel hydrides with high ${T}_{c}$ at low pressure, even ambient pressure. Here, we propose a strategy that elements with little electronegativity, large atomic volume, and suitable valence electron number can be regarded as a candidate for reducing the stable pressure by summarizing the superconducting rules of the clathrate hexahydrides, and find that thorium is a good ``precompressor.'' Based on the above strategy, we doped thorium into clathrate hexahydrides with a ${\mathrm{H}}_{24}$ cage, and designed a series of hydrides. They could be dynamically stable at moderate pressure, which is much lower than that of the well-known hexahydrides $\mathrm{Ca}{\mathrm{H}}_{6}$. Remarkably, $\mathrm{LaT}{\mathrm{h}}_{3}{\mathrm{H}}_{24}, \mathrm{AcT}{\mathrm{h}}_{3}{\mathrm{H}}_{24}$, and $\mathrm{YTh}{\mathrm{H}}_{12}$ exhibit excellent superconductivity with high ${T}_{c}$ of 198 K at 50 GPa, 201 K at 60 GPa, and 208 K at 60 GPa, respectively. This work suggests that thorium doping is an effective method for finding hydrides with high ${T}_{c}$ at moderate pressure, and successfully helps us design a series of interesting high-temperature superconducting hydrides.