Abstract The hole-doped organic superconductor κ-(ET) 4 Hg 3-δ Br 8 , (κ-HgBr), where δ=11% and ET=bis(ethylenedithio)tetrathiafulvalene, has been the key to bridge knowledge gap between half-filled organics doped cuprate systems. Nonetheless, isotropic triangular lattice of ET dimers κ-HgBr is responsible for magnetic susceptibility its superconductivity. We have measured zero-field (ZF) muon ...