Superconductivity nearby quantum critical region in hole-doped organic strange metal κ-(ET)4Hg3-δBr8, δ=11

• Published in: Journal of physics. Conference series 2023-03, Vol.2462 (1), p.012061
• Main Authors: Sari, D P, Kaito, M, Someya, Y, Widyaiswari, U, Watanabe, I, Taniguchi, H, Ishii, Y
• Format: Article
• Language: English
• Subjects: Coupling; Critical field (superconductivity); Magnetic permeability; Muon spin relaxation; Organic superconductors; Penetration depth; Physics; Superconductivity
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/2462/1/012061

The hole-doped organic superconductor κ-(ET)4Hg3-δBr8, (κ-HgBr), where δ=11% and ET=bis(ethylenedithio)tetrathiafulvalene, has been the key to bridge the knowledge gap between half-filled organics and doped cuprate systems. Nonetheless, the isotropic triangular lattice of ET dimers of κ-HgBr is responsible for the magnetic susceptibility and its superconductivity. We have measured zero-field (ZF) muon spin relaxation-rotation (µ+SR) in κ-HgBr showing the ZF-µ+SR relaxation rate from temperature around 10 K down to 0.3 K is temperature-independent. This is consistent with a superconducting state that preserved time-reversal symmetry. There was almost no change in the maximally 100 Oe of transverse-field-µ+SR time spectra, at 0.3 K and above superconducting temperature, Tc~4.6(3) K. This suggests that the in-plane London penetration depth, λbc, is longer than a μm order, while we estimate the lower limit of the lower critical field, Hc1, to be 30 Oe, although, however, the measurement using another geometric setup is necessary to determine the absolute value of λbc. These could be an indication of a strong-coupling superconductor. A possible mechanism of preserved time-reversal Cooper pairing formation from strong-coupling non-FL metal with geometrical frustration is discussed.