Effect of spin-orbit coupling on the superconductivity in the lead hydrides under high pressure

Abstract

The spin-orbit coupling (SOC) effect of heavy elements has the capacity to influence the electron structure and properties of materials. Previous studies have demonstrated that the SOC effect enhances the electron-phonon coupling constant (EPC λ) of elemental Pb and Pb-containing compounds in theory. However, the opposite phenomenon is found in the hydrides of lead that we studied, i.e., the SOC effect reduced the EPC λ. Moreover, previous studies have not clearly elucidated the underlying physical mechanism through which SOC effects impact superconductivity. Furthermore, the effects of SOC in Pb-H compounds under high pressure remain unexplored. Here, we investigated the structures of the Pb-H system and the EPC mechanism under the action of SOC at pressures. A new P21/m−PbH2 hydride has been discovered to be more stable under high pressure than previously reported. The new lead superhydrides have been identified, including Cmcm-PbH10, which contains a linear H4 macromolecule with double covalent bonds. The superconducting critical temperature (Tc) of lead superhydrides is significantly lower than that of YH10 and LaH10. This is due to the fact that hydrogen exists in the form of a large number of H2 molecules without forming a cagelike supramolecular structure. In Pb, in addition to the previously reported reason of phonon softening, we have identified another important factor contributing to the increase in EPC λ: the enhancement of the average electron-phonon interaction at the Fermi surface due to the SOC effect. In Pb-H compounds, the SOC effect leads to the topological transformation of the Fermi surface, and increases the probability of charges appearing near H-H bonds and the twisting vibration frequency of hydrogen molecules, which is the important reason for the decline of EPC λ. In the Pb-H system, the SOC effect can result in an increase in the average phonon frequency and a decrease in EPC λ. The superconducting Tc is dependent upon the competition between the decreased EPC λ and the increased Debye temperature.

Source-reported materials — not catalogue approval

Similar papers