Anisotropic phase stiffness in infinite-layer nickelates superconductors

• Published in: Nature communications Vol. 16; no. 1; pp. 6780 - 9
• Main Authors: Xu, Minyi, Qiu, Dong, Xu, Minghui, Guo, Yehao, Shen, Cheng, Yang, Chao, Sun, Wenjie, Nie, Yuefeng, Li, Zi-Xiang, Xiang, Tao, Qiao, Liang, Xiong, Jie, Li, Yanrong
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 23.07.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 147/137; 639/766/119/1003; 639/766/119/2795; Anisotropy; Broken symmetry; Crystal lattices; Cuprates; Electrical conductivity; Electrical resistivity; Electrons; Energy costs; Fluids; Group 5A compounds; Humanities and Social Sciences; Magnetic fields; multidisciplinary; Phase variations; Science; Science (multidisciplinary); Stiffness; Superconductivity; Superfluidity; Symmetry; Temperature; Thin films; Unconventional superconductors; Vector currents
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-025-61654-9

In unconventional superconductors such as cuprates and iron pnictides and chalcogenides, phase stiffness—a measure of the energy cost associated with superconducting phase variations—governs the formation of superconductivity. Here we demonstrate a vector current technique enabling in-situ angle-resolved transport measurements to reveal anisotropic phase stiffness in infinite-layer nickelate superconductors. Pronounced anisotropy of in-plane resistance manifests itself in both normal and superconducting transition states, indicating crystal symmetry breaking. Remarkably, the electric conductivity of Nd 0.8 Sr 0.2 NiO 2 peaks at 125° between the direction of the current and crystal principal axis, but this angle evolves to 160° near zero-resistance temperature. Further measurements reveal that the phase stiffness maximizes along 160°, a direction distinct from the symmetry axis imposed by both electronic nematicity and the crystal lattice. Identical measurements conducted on a prototypical cuprate superconductor yield consistent results. By identifying the contrasting anisotropy between electron fluid and superfluid in both nickelates and cuprates, our findings provide clues for a unified framework for understanding unconventional superconductors. The authors study nickelate superconductor Nd0.8Sr0.2NiO2 by angle-dependent transport. They find that the superconducting phase stiffness is anisotropic, and that electrical conductivity peaks along the direction with maximized phase stiffness.