Presentation Information
[9a-A31-5]Theoretical Study of Atomic Substitution Effects on the Critical Pressure in Nickelate Superconductivity
〇(M2)Tomohiko Hamada1, Kensei Ushio1, Kuroki Kazuhiko2, Hirofumi Sakakibara1,3 (1.Fac. of Eng., Tottori Univ, 2.Dept. of Phys., Univ. of Osaka, 3.AMES, Tottori Univ)
Keywords:
superconductor,nickelate superconductor,high-temperature superconductivity
The recently discovered bilayer nickelate superconductor La3Ni2O7 has attracted significant attention as a new platform for high-temperature superconductivity because of its remarkably high transition temperature, Tc≈ 90 K. However, its superconducting phase emerges only under high pressure, which limits practical applications. One possible origin of the absence of superconductivity at ambient pressure is the distortion of the interlayer Ni–O–Ni bond connecting the two NiO2 layers. Previous experimental studies have suggested that either a straight Ni–O–Ni bond angle (α=180°) or a tetragonal crystal structure with I4/mmm symmetry is a necessary condition for superconductivity.
Motivated by this empirical trend, Ochi et al. proposed Sr3Ni2O5Cl2 as a bilayer nickelate with α = 180 deg at ambient pressure. In this compound, substitution of La by the larger Sr ion suppresses the displacement of the apical oxygen and straightens the Ni–O–Ni bond. Experiments subsequently confirmed α=180° under ambient conditions. Nevertheless, no superconducting transition has been observed, possibly because of crystal defects such as stacking faults induced by chloride ions.
In this study, we aim to design bilayer nickelates that can realize superconductivity at ambient or low pressure. Inspired by the above strategy, we investigate partial substitution of the La site in La3Ni2O7 with larger rare-earth ions to stabilize a tetragonal structure and achieve α=180°. Since the proposed materials are oxide, stacking-fault problems may be exempted. We systematically examine the relationship between ionic radius and bond angle α and evaluate the dynamical stability of the tetragonal phase using phonon calculations. Based on these analyses, we identify promising substituent elements and substitution ratios that stabilize the tetragonal structure at ambient pressure. We will also present theoretical predictions of Tc based on first principles and many-body electron calculations.
Motivated by this empirical trend, Ochi et al. proposed Sr3Ni2O5Cl2 as a bilayer nickelate with α = 180 deg at ambient pressure. In this compound, substitution of La by the larger Sr ion suppresses the displacement of the apical oxygen and straightens the Ni–O–Ni bond. Experiments subsequently confirmed α=180° under ambient conditions. Nevertheless, no superconducting transition has been observed, possibly because of crystal defects such as stacking faults induced by chloride ions.
In this study, we aim to design bilayer nickelates that can realize superconductivity at ambient or low pressure. Inspired by the above strategy, we investigate partial substitution of the La site in La3Ni2O7 with larger rare-earth ions to stabilize a tetragonal structure and achieve α=180°. Since the proposed materials are oxide, stacking-fault problems may be exempted. We systematically examine the relationship between ionic radius and bond angle α and evaluate the dynamical stability of the tetragonal phase using phonon calculations. Based on these analyses, we identify promising substituent elements and substitution ratios that stabilize the tetragonal structure at ambient pressure. We will also present theoretical predictions of Tc based on first principles and many-body electron calculations.