Journal de Physique I

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DOI: 10.1051/jp1:1996178
J. Phys. I France 6 (1996) 1609-1630

Physical Properties of Some ET-Based Organic Metals and Superconductors with Mercury Containing Anions

R.B. Lyubovskii, R.N. Lyubovskaya and O.A. Dyachenko

Institute of Chemical Physics RAS. Chernogolovka, MD 142432 Russia

(Received 6 April 1996, accepted 11 June 1996)

Abstract
Because of mercury atoms capability of forming the compounds with various coordination, the application of the electrolytes with Hg containing anions in electrochemical oxidation of ET (bis(ethylenedithio)tetrathiafulvalene) results in the formation of ET salts with the anions of different composition. The properties of organic metals and superconductors are briefly described for three families: 1) ET ₄Hg $_{3-\delta}$ X ₈ (( $\delta < 0.3,\,$ X = Cl, Br, I)2) (ET) ₂[ Hg(SCN) _3-nX _n] (X = F, Br, I for n=1, X = Cl for $n=1,2),\,3$ ) (ET) ₈[ Hg ₄X ₁₂(C ₆H ₅Y)(X, Y = Cl, Br). The superconductivity of (ET) ₂[ Hg(SCN)Cl ₂] under pressure about 9 kbar with $T_{\rm onset}=2$ K is reported for the first time. The coexistence of two incommensurate sublattices in the salts of ET ₄Hg $_{3-\delta}$ X ₈ family probably gives rise to their unusual physical properties such as an abnormally high anisotropy of conductivity together with its growth with temperature drop, a positive curvature of the upper critical magnetic field, $H_{\rm c2}$ , and an exceeding of Clogston paramagnetic limit, the invalidity of Korringa law for the temperature dependence of spin-lattice relaxation rate, the growth of the temperature of a superconducting transition $T_{\rm c}$ with pressure, ${\rm d}T_{\rm c}/{\rm d}p>0$ , and a series of other peculiarities. Shubnikov-de Haas oscillations were observed for some salts of (ET) ₈[ Hg ₄X ₁₂(C ₆H ₅Y) ₂] family. The possible types of Fermi surface are discussed for these salts.