[PC3] Novel materials, Nickelates

6:15 PM - 6:45 PM JST(9:15 AM - 9:45 AM UTC)

[PC3-03-INV] The Quest for High Temperature Superconducting Nickelates

*Ariando Ariando¹ (1. National University of Singapore (Singapore))

Keywords:

Nickelate

The discovery of superconductivity in the Ba-La-Cu-O system (the cuprate) at around 30 K marked a major breakthrough, spurring extensive exploration of oxide-based layered superconductors to achieve even higher critical temperatures (T_c) and to understand their electron pairing mechanisms. Until recently, evidence of Cooper pairing above 30 K in systems isostructural to the cuprates but without copper, under ambient pressure, and without lattice compression, had remained elusive despite observations of superconductivity in nickel oxide-based compounds (the nickelates). In this talk, I will present our efforts in designing and understanding higher-temperature superconducting nickelates. We demonstrate a new superconducting infinite-layer nickelate, with a T_c approaching 40K under ambient pressure, realized in d⁹ hole-doped, late rare-earth nickel oxide (Sm-Eu-Ca)NiO₂ thin films with negligible lattice compression. This is supported by observations of a zero-resistance state above 31 K and the Meissner effect. The material can be synthesized with essentially no Ruddlesden–Popper-type structural defects, and it exhibits ultralow resistivity of approximately 0.01 mΩ·cm and a residual resistivity ratio of up to 10. Using resonant inelastic x-ray scattering, we observe dispersive paramagnonic excitations in both optimally and overdoped (Sm-Eu-Ca)NiO₂ samples, supporting a spin-fluctuation-mediated pairing scenario. Notably, despite a two-fold enhancement of T_c in (Sm-Eu-Ca)NiO₂ nickelates compared to their Pr- or Nd-based counterparts, the effective exchange coupling strength is reduced by approximately 20 percent. This behavior contrasts with hole-doped cuprates, where magnetic interactions are positively correlated with T_c, highlighting key differences in their superconducting mechanisms. Our findings demonstrate the potential for achieving high-temperature superconductivity in strongly correlated d-electron metal oxides beyond copper, offering a promising platform for further investigation into the nature of high-temperature Cooper pairing.