Electron–phonon coupling and superconductivity in an alkaline earth hydride CaH6 at high pressures. (1st August 2022)

• Record Type: Journal Article
• Authors: Jeon, Hyunsoo; Wang, Chongze; Liu, Shuyuan; Bok, Jin Mo; Bang, Yunkyu; Cho, Jun-Hyung
• Is Part Of: New journal of physics. Volume 24:Number 8(2022)
• Publication Date: 2022-08-01
• Subjects: superconductivity -- alkaline earth -- superhydride; Physics -- Periodicals; Physics; Periodicals; 530.05
• DOI: 10.1088/1367-2630/ac8a0c
• Languages: English
• ISSNs: 1367-2630

Abstract

Abstract: Recently, an alkaline earth hydride CaH6 having a sodalitelike clathrate structure has been experimentally synthesized at megabar pressures with a maximum T c of 215 K, comparable to that of a rare earth hydride LaH10 . Here, based on first-principles calculations, we find that CaH6 exhibits a huge peak in the Eliashberg spectral function α 2 F around the low-frequency region of H-derived phonon modes, in contrast to LaH10 having a widely spreading spectrum of α 2 F over the whole frequencies of H-derived phonon modes. It is revealed that the huge peak of α 2 F in CaH6 is associated with an effective electron–phonon coupling (EPC) between low-frequency optical phonons and hybridized H 1 s and Ca 3 d states near the Fermi energy. As pressure increases, the strengthened H–H covalent bonding not only induces a hardening of optical phonon modes but also reduces the electron–phonon matrix elements related to the low-frequency optical modes, thereby leading to a lowering of the EPC constant. It is thus demonstrated that H-derived low-frequency phonon modes play an important role in the pressure-induced variation of T c in CaH6 . Furthermore, unlike the presence of two distinct superconducting gaps in LaH10, CaH6 is found to exhibit a single isotropic superconducting gap.