biostudies-literatureLiu SBNational Natural Science Foundation of ChinaNational Key Research and Development Program of ChinaInnovation Program for Quantum Science and Technologynwae220https://www.ebi.ac.uk/biostudies/studies/S-EPMC11562829biostudies-literatureUnknown11(12)The quantum Griffiths singularity (QGS) is a phenomenon driven by quenched disorders that break conventional scaling invariance and result in a divergent dynamic critical exponent during quantum phase transitions (QPT). While this phenomenon has been well-documented in low-dimensional conventional superconductors and in three-dimensional (3D) magnetic metal systems, its presence in 3D superconducting systems and in unconventional high-temperature superconductors (high-<i>T</i> _c SCs) remains unclear. In this study, we report the observation of robust QGS in the superconductor-metal transition (SMT) of both quasi-2D and 3D anisotropic unconventional high-<i>T</i> _c superconductor CaFe_1- <i>_x</i> Ni <i>_x</i> AsF (<i>x</i> <5%) bulk single crystals, where the QGS states persist to up to 5.3 K. A comprehensive quantum phase diagram is established that delineates the 3D anisotropic QGS of SMT induced by perpendicular and parallel magnetic fields. Our findings reveal the universality of QGS in 3D superconducting systems and unconventional high-<i>T</i> _c SCs, thereby substantially expanding the range of applicability of QGS.National science reviewThree-dimensional quantum Griffiths singularity in bulk iron-pnictide superconductors.PMC1156282992265106119340012019YFA03084022021ZD030240311921005Li JChen MFeng YCui JSui YGuan STian CWei XChen JHChen CZhao YHao TJia SZhang YCai YCui HLiu SBSong YfalseThree-dimensional quantum Griffiths singularity in bulk iron-pnictide superconductors.The quantum Griffiths singularity (QGS) is a phenomenon driven by quenched disorders that break conventional scaling invariance and result in a divergent dynamic critical exponent during quantum phase transitions (QPT). While this phenomenon has been well-documented in low-dimensional conventional superconductors and in three-dimensional (3D) magnetic metal systems, its presence in 3D superconducting systems and in unconventional high-temperature superconductors (high-<i>T</i> _c SCs) remains unclear. In this study, we report the observation of robust QGS in the superconductor-metal transition (SMT) of both quasi-2D and 3D anisotropic unconventional high-<i>T</i> _c superconductor CaFe_1- <i>_x</i> Ni <i>_x</i> AsF (<i>x</i> <5%) bulk single crystals, where the QGS states persist to up to 5.3 K. A comprehensive quantum phase diagram is established that delineates the 3D anisotropic QGS of SMT induced by perpendicular and parallel magnetic fields. Our findings reveal the universality of QGS in 3D superconducting systems and unconventional high-<i>T</i> _c SCs, thereby substantially expanding the range of applicability of QGS.2024-01-01T00:00:00Z2024 Dec2025-04-04T02:33:57.651Z2025-04-04T02:33:57.651ZS-EPMC115628293955422810.1093/nsr/nwae220