13:30 〜 13:45
▲ [23p-D215-1] The systematic study on the stability and superconductivity of Y-Mg-H compounds under high pressure
キーワード：superconductivity, electron-phonon coupling, Superconducting phase transition
Recently, with the experimental verification of room temperature superconductivity in C-S-H compounds (Tc ∼ 288K at ∼ 267GPa), ternary hydrides have been playing an increasingly important role in the search for novel high-temperature superconductors. Here we have investigated structural stabilities of high-pressure YMgHx phases ( x = 2 ∼ 10, 12, 14, and 16) and their superconductivities by employing evolutionary-algorithm-based crystal search combined with first-principles calculations. For predicted candidate structures of YMgHx, our convex hull and phonon analyses revealed seven stable and two metastable phases. For all the predicted phases, we also predicted superconducting transition temperatures (Tc) by using the McMillun formula. We found P4/mmm-YMgH6 having Tc = 76 K at 300 GPa comparable to the boiling temperature of liquid nitrogen, and high-Tc (≥ 77 K) being predicted for the H-richer phases, P4/mmm-YMgH8 (124 K at 300 GPa), Cmmm-YMgH12 (152 K at 250 GPa), and Fd-3m-YMgH12 (190 K at 200 GPa), which possess clathrate structures composed of H14, H18, H24, and H24 cages, respectively. To elucidate why the H-rich phases attain high-Tc, we analyzed electronic and phonon band structures as well as electron-phonon coupling strength based on Eliashberg spectral functions. The clathrate structures exhibit both a larger H-driven electronic density of states at the Fermi level and a denser H-driven phonon density of states, correlating with larger EPC constants. Our structural and chemical bonding analyses have revealed that the highest-Tc phase Fd-3m-YMgH12 has H4 units formed in the sodalite cage.