Three-dimensional quantum Griffiths singularity in bulk iron-pnictide superconductors

TL;DR

This study demonstrates the presence of quantum Griffiths singularity in 3D high-temperature superconductor CaFe1-xNixAsF, revealing its universality in unconventional superconducting systems and expanding understanding of quantum phase transitions.

Contribution

First observation of robust quantum Griffiths singularity in 3D high-Tc superconductor CaFe1-xNixAsF, establishing its universality in 3D superconducting systems.

Findings

Quantum Griffiths singularity persists up to 5.3 K in CaFe1-xNixAsF.

Quantum phase diagram shows 3D anisotropic QGS induced by magnetic fields.

QGS observed in both quasi-2D and 3D anisotropic high-Tc superconductors.

Abstract

The quantum Griffiths singularity (QGS) is a phenomenon driven by quenched disorders that break conventional scaling invariance and result in a divergent dynamical 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-Tc 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-Tc superconductor CaFe1-xNixAsF (x < 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 field. Our findings reveal the universality of QGS in 3D superconducting systems and unconventional high-Tc SCs, thereby substantially expanding the range of applicability of QGS.