Under the high pressure around 20 GPa, nickelate superconductor La₃Ni₂O₇ (Tc~80K) was discovered [1,2]. This superconductor attracts much attention due to similarity of crystal structure to high-Tc cuprate such as La₂SrCu₂O₆. La₃Ni₂O₇ corresponds to the n = 2 type of the Ruddlesden-Popper phase represented by the general formula of La_n+1Ni_nO_3n+1, and particularly, La₄Ni₃O₁₀, is corresponding to n = 3 type of the Ruddlesden-Popper phase having triple layers of NiO₂ plane. Due to the similarity of band structure between those materials, we expect superconductivity in La₄Ni₃O₁₀ under high pressure [3]. We synthesized polycrystalline samples of La₃Ni₂O₇ and La₄Ni₃O₁₀ and measure the temperature dependence of resistance under high pressure. Then we successfully discovered new superconductor La₄Ni₃O₁₀ under high pressure [3-5].

We have synthesized La₃Ni₂O₇ and La₄Ni₃O₁₀ samples with different oxygen contents and examined the superconducting properties of both samples. La₃Ni₂O₇ shows almost the same Tc around 26GPa. However, dome-like property appears with increasing pressure [4]. Particularly, La₄Ni₃O₁₀, shows strong oxygen contents dependence of transition temperature, and Tc exceed 36K at 48GPa [5]. We also perform NMR measurements to understand the local structure and mechanism of superconductivity. In my presentation, I will give a talk about detailed superconducting properties of nickelate superconductors including NMR analysis.

References
[1] H. Sun et al., Nature 621, 493 (2023).
[2] M. Nakata et al., Phys. Rev. B 95, 214509 (2017).
[3] H. Sakakibara et al., Phys. Rev. B 109, 144511 (2024).
[4] Y. Ueki et al., J. Phys. Soc. Japan. 94, 013703 (2024).
[5] H. Nagata et al., J. Phys. Soc. Japan 93, 095003 (2024)