Quantum Griffiths Singularity in a Layered Superconducting Organic–Inorganic Hybrid Superlattice

Quantum Griffiths singularity (QGS) is among the remarkable phenomena induced by disorder in quantum phase transitions (QPTs). In recent years, experimental progresses have been made in ultrathin superconducting films. However, there is still lack of approaches to trigger QGS in bulk superconductors. Herein, we develop a charge-induced disorder introduction process to trigger QGS in organic-inorganic hybrid superlattices. Large-sized organic cations are intercalated into layered inorganic crystal, which leads to electron doping and thus quasi-two-dimensional superconductivity. The charge transfer between inorganic layers and interlayer cations introduces charge disorder into the hybrid superlattice without destroying lattice integrality. Consequently, QGS emerges in the bulk superconducting superlattice. Furthermore, deviation of phase boundary from the Werthamer–Helfand–Hohenberg theory indicates relatively strong spin-orbit coupling. The observation provides a new pathway to investigate QPTs in disordered systems and reveals universality of QGS in superconductors.