Failed superconductivity in a Mott spin liquid material

Unconventional superconductivity often emerges in complex materials in which competing orders and complicated band structure obscure its origin. Quasi-two-dimensional organic Mott spin liquids, in contrast, provide a simple, single-band platform in the absence of other orders. Here we show that in chemically substituted κ -organics, superconductivity never achieves global coherence, even as temperature T → 0. Instead, we reveal the presence of superconducting domains embedded in a percolating metallic background that undergo a magnetic field-tuned quantum superconductor-to-metal transition, followed by the surprising emergence of universal conductance fluctuations in macroscopic samples. Our findings demonstrate that failed superconductivity arises from the interplay of intrinsic inhomogeneity and quantum phase fluctuations, providing a new perspective on anomalous metallic states observed in cuprates, disordered thin films, and oxide interfaces.