Potential high-temperature superconductivity in the substitutional alloy of (Y,Sr)H11 under high pressure

The recently synthesized ${\mathrm{SrH}}_{22}$, with a rich amount of ${\mathrm{H}}_{2}$ units, is predicted with low superconductivity, since two hydrogen (H) atoms in ${\mathrm{H}}_{2}$ units are inclined to stay together by forming a well-known sigma bond, where H electrons tend to occupy the low-lying energy level far below the Fermi energy, resulting in a less H populated Fermi surface. Of particular interest, for ${\mathrm{SrH}}_{22}$ or other similar ${\mathrm{H}}_{2}$-rich hydrides, is to optimize the H electron density of states in the search for high superconductivity. Here, via the strategy of bringing an additional metal element into the binary hydride, in combination with our developed global structure-searching method, we predict a ternary hydride of ${\mathrm{YSrH}}_{22}$. Compared with the parent hydride of ${\mathrm{SrH}}_{22}$, the H electron density of states at the Fermi level of ${\mathrm{YSrH}}_{22}$ is significantly enhanced, due to the favorable charge transfer from metal elements, such as Y, to the antibonding state of the sigma bond of ${\mathrm{H}}_{2}$, where such a bond is broken and H electrons come back to the Fermi surface. Our in-depth analysis indicates that this hydride could be viewed as a substitutional alloy superhydride of $(\mathrm{Y},\mathrm{Sr}){\mathrm{H}}_{11}$ with an estimated superconducting critical temperature ${T}_{c}$ of 240 K at 175 GPa, which is much higher than that of ${\mathrm{SrH}}_{22}$ (${T}_{c}=21\phantom{\rule{0.28em}{0ex}}\mathrm{K})$ and ${\mathrm{LaH}}_{11}$ (${T}_{c}=13\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) both at 200 GPa. Our current findings not only offer a platform to tune the superconductivity of binary superhydrides ${\mathrm{SrH}}_{22}$ and ${\mathrm{LaH}}_{11}$, via the strategy of metal element doping, but also provide a roadmap in the search for high superconductivity, even toward room-temperature superconductivity, in the family of ternary alloy superhydrides.