Recovery of the metallic state and quantum oscillations in a dielectric salt of the $\mathrm{(ET)_8[Hg_4X_{12}(C_6H_5Y)_2]}$ family at $\mathrm X=\mathrm Y=\mathrm{Br}$ under compression

The quasi-two-dimensional organic conductor (ET)₈[Hg₄Br₁₂(C₆H₅Br)₂] (ET is bis(ethylenedithio)tetrathiafulvalene) undergoes a metal-insulator phase transition at T ~ 170 K. It has been shown that a pressure of 8 kbar suppresses this transition and holds a metallic state to liquid-helium temperatures. Shubnikov—de Haas quantum oscillations with the single frequency F = 215 T have been observed in a magnetic field up to 15 T. The properties of this salt are compared to the properties of the (ET)₈[Hg₄Cl₁₂(C₆H₅Cl)₂] salt of the same family. Time annealing provides an important effect on the conducting properties of the salt under investigation.