Critical role of hydrogen for superconductivity in nickelates

Xiang Ding, Charles C. Tam, Xuelei Sui, Yan Zhao, Minghui Xu, Jaewon Choi, Huaqian Leng, Ji Zhang, Mei Wu, Haiyan Xiao, Xiaotao Zu, Mirian Garcia-Fernandez, Stefano Agrestini, Xiaoqiang Wu, Qingyuan Wang (), Peng Gao, Sean Li, Bing Huang (), Ke-Jin Zhou () and Liang Qiao ()
Additional contact information
Xiang Ding: University of Electronic Science and Technology of China
Charles C. Tam: Harwell Campus
Xuelei Sui: Beijing Computational Science Research Center
Yan Zhao: University of Electronic Science and Technology of China
Minghui Xu: University of Electronic Science and Technology of China
Jaewon Choi: Harwell Campus
Huaqian Leng: University of Electronic Science and Technology of China
Ji Zhang: University of New South Wales
Mei Wu: Peking University
Haiyan Xiao: University of Electronic Science and Technology of China
Xiaotao Zu: University of Electronic Science and Technology of China
Mirian Garcia-Fernandez: Harwell Campus
Stefano Agrestini: Harwell Campus
Xiaoqiang Wu: Chengdu University
Qingyuan Wang: Chengdu University
Peng Gao: Peking University
Sean Li: University of New South Wales
Bing Huang: Beijing Computational Science Research Center
Ke-Jin Zhou: Harwell Campus
Liang Qiao: University of Electronic Science and Technology of China

Nature, 2023, vol. 615, issue 7950, 50-55

Abstract: Abstract The newly discovered nickelate superconductors so far only exist in epitaxial thin films synthesized by a topotactic reaction with metal hydrides1. This method changes the nickelates from the perovskite to an infinite-layer structure by deintercalation of apical oxygens1–3. Such a chemical reaction may introduce hydrogen (H), influencing the physical properties of the end materials4–9. Unfortunately, H is insensitive to most characterization techniques and is difficult to detect because of its light weight. Here, in optimally Sr doped Nd0.8Sr0.2NiO2H epitaxial films, secondary-ion mass spectroscopy shows abundant H existing in the form of Nd0.8Sr0.2NiO2Hx (x ≅ 0.2–0.5). Zero resistivity is found within a very narrow H-doping window of 0.22 ≤ x ≤ 0.28, showing unequivocally the critical role of H in superconductivity. Resonant inelastic X-ray scattering demonstrates the existence of itinerant interstitial s (IIS) orbitals originating from apical oxygen deintercalation. Density functional theory calculations show that electronegative H– occupies the apical oxygen sites annihilating IIS orbitals, reducing the IIS–Ni 3d orbital hybridization. This leads the electronic structure of H-doped Nd0.8Sr0.2NiO2Hx to be more two-dimensional-like, which might be relevant for the observed superconductivity. We highlight that H is an important ingredient for superconductivity in epitaxial infinite-layer nickelates.

Date: 2023
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DOI: 10.1038/s41586-022-05657-2

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