Fermi surface topology and anisotropic superconducting gap in electron-doped hydride compounds at high pressure

The recent theoretical discovery of the predicted high-temperature superconductivity (superconducting transition temperature T-c similar to 351 K at 300 GPa) in clathrate Li2MgH16 is an important advance toward room-temperature superconductors. Here we use first-principle approaches to identify a new ternary hydride of clathrate structure of Fd (3) over barm-Rb2MgH16 by Rb-doped MgH16 at 300 GPa. We first verified the thermal and dynamic stability for the Fd (3) over barm-Rb(2)MgH(16 )through the formation enthalpy and phonon calculations, respectively. Next, we showcased that Fd (3) over barm-Rb2MgH16 has two Fermi surface (FS) sheets, which are both dominated by the H2 s orbital. Using the Eliashberg formalism, the T-c of Fd (3) over barm-Rb2MgH16 was calculated to be 130 K at 300 GPa. Furthermore, the calculations of the electronic, phonon, and superconducting properties reveal that Fd (3) over barm-Rb2MgH16 has four FS sheets with mixed H1 s and H2 s orbital character and reaches the T-c of 352 K at 300 GPa. Compared with Fd (3) over barm-Rb2MgH16, Fd (3) over barm-Li(2)MgH(16 )produces high-frequency phonon softening, leading to the enhancement of K. Moreover, it is demonstrated that Rb substitution for Li produces the reduction of contribution of H orbitals to the FS sheets and the decrease in FS sheets in number, which tend to decrease the electron-phonon coupling strength and T-c. Our observed FS sheets and their associated superconducting gap will provide key insights into the understanding of the superconductivity mechanism in these and related systems.