Superconductivity nearby quantum critical region in hole-doped organic strange metal κ-(ET)₄Hg_3-δBr₈, δ=11%

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 spin relaxation-rotation (µ + SR) in showing ZF-µ SR relaxation rate from temperature around 10 K down 0.3 temperature-independent. This consistent with a superconducting state that preserved time-reversal symmetry. There was almost no change maximally 100 Oe transverse-field-µ time spectra, at above temperature, T c ~4.6(3) K. suggests in-plane London penetration depth, λ bc longer than μm order, while we estimate lower limit critical field, H c1 be 30 Oe, although, however, measurement using another geometric setup necessary determine absolute value . These could an indication strong-coupling superconductor. A possible mechanism Cooper pairing formation non-FL metal geometrical frustration discussed.