Elbio Dagotto
University of Tennessee, Knoxville and Materials Science and Technology Division, Oak Ridge National Laboratory
In 2023, news spread that a Ni-based bilayer oxide superconductor had been found with a Tc of 80 K, starting the current frenzy of Ni high-Tc superconductivity [1]. The chemical formula is La3Ni2O7 (LNO). Although superconductivity in LNO was originally achieved at high pressure, compressive strain has been recently shown to produce thin films that superconduct at ambient pressure with record Tc ~ 63K [2]. My presentation will start with a quick review of the precursors of the present frenzy: Ni-based thin films of the infinite-layer phase [3]. Theoretical developments by several groups have unveiled a Fermi surface in bilayers where a distinct feature emerges: a so-called g-pocket at M = (p,p), which appears to be one-to-one linked to superconductivity [4]. In addition to this feature, other differences with high-Tc cuprates were unveiled, such as the formation of “dimers” in between the NiO2 planes of the bilayer (Ni oxide trilayers [5] may also be discussed here, time allowing). The most recent theory developments address superconductivity in ultra-thin films. Our work suggests a possible change in the pairing channel from s to d when moving from high pressure to high compressive stress [6], but other groups find s wave in both cases. Although I will focus on only a handful of experimental and theoretical results, the publications of our group contain vast literature that interested readers can consult for a balanced perspective on the subject. The field of Ni-oxide superconductivity is rapidly evolving, and surprises appear often in the arXiv, rendering this area exciting and one of the hottest topics of research in present day Condensed Matter Physics.
[1] H. Sun, …, and M. Wang, Nature 621, 493 (2023). N. Wang, …, and J. Cheng, Nature 634, 579 (2024).
[2] E.K. Ko et al. Nature 638, 935 (2025); G. Zhou et al. Nature 640, 641 (2025); Y. Tarn et al., arXiv:2512.04708.
[3] D. Li, …, and H. Hwang, Nature 572, 624 (2019).
[4] Y. Zhang et al., Nat Commun 15, 2470 (2024) and references therein. See also Y. Zhang et al., PRB 108, L180510 (2023); PRB 108, 165141 (2023); L.-F. Lin et al., PRB 110, 195135 (2024); Y. Zhang et al., PRB 109, 045151 (2024). Other theory groups arrived at similar conclusions independently. See citations in our publications.
[5] Y. Zhu, …, and J. Zhao, Nature 631, 531 (2024); Y. Zhang et al., PRL 133, 136001 (2024).
[6] Y. Zhang et al., arXiv:2512.19520 and references therein.