Enhanced Superconductivity and Mixed-dimensional Behaviour in Infinite-layer Samarium Nickelate Thin Films
cond-mat.supr-con
/ Authors
Mingwei Yang, Heng Wang, Jiayin Tang, Junping Luo, Xianfeng Wu, Wenjing Xu, Aile Wang, Yuetong Wu, Ruilin Mao, Ze Wang
and 17 more authors
Zhicheng Pei, Guangdi Zhou, Zhengang Dong, Bohan Feng, Lingchi Shi, Wenjie Meng, Chuanying Xi, Li Pi, Qingyou Lu, Jun Okamoto, Hsiao-Yu Huang, Di-Jing Huang, Haoliang Huang, Qisi Wang, Peng Gao, Zhuoyu Chen, Danfeng Li
/ Abstract
Rare-earth infinite-layer nickelates represent an emerging class of unconventional superconductors, with materials synthesis largely limited to early lanthanide compounds. Here, we report the synthesis and characterization of phase-pure superconducting samarium-based infinite-layer nickelate thin films, including the first demonstration of Sm$_{1-x}$Sr$_x$NiO$_2$, along with co-doped variants incorporating europium and calcium. These films, grown on LSAT (001) substrates, exhibit coherent lattice structures up to $\sim$ 9 nm thickness with minimal stacking faults. The co-doped compounds achieve a record-small $c$-axis parameter of 3.26 Å and display remarkable superconducting transition temperatures up to 32.5 K. These results establish a clear correlation between decreasing $c$-axis parameter and increasing critical temperature across different rare-earth systems. In addition, angle-dependent magnetoresistance investigations reveal the existence of a hybrid mixture of 2D and 3D superconductivity in this novel system with enhanced coupling between the rare-earth 5d and Ni 3d orbitals, confirmed by resonant inelastic X-ray scattering experiments. As the concentration of Eu increases, the system exhibits a clear tendency towards 3D superconductivity. Furthermore, we observe distinctive negative magnetoresistance in the europium-containing samples. These findings advocate clear materials design principles for higher transition temperatures and exotic physics in infinite-layer nickelate superconductors through structural engineering of the rare-earth site.