V.N. Laukhin

Magnetic field studies of the peculiar electronic state in the /spl alpha/-(BEDT-TTF)/sub 2/MH/sub g/(SCN)/sub 4/ family

Summary form only given. The variety of magnetoresistance (MR) anomalies exhibited by the members of the /spl alpha/-(BEDT-TTF)/sub 2/MH/sub g/(SCN)/sub 4/ family with M=Tl, K or Rb is reviewed in the connection with possible modification of their electronic structure at low temperatures. Special attention is paid to the angular MR oscillations (AMRO) which provide indispensable information about the Fermi surface (FS). Two different types of AMRO are observed above and below the phase transition temperature, T/sub p/, respectively. The high-temperature AMRO are associated with the cylindrical FS enabling us to deduce the cylinder cross-section. At the same time, the low-temperature AMRO reveal an occurrence of a specific plane in the electronic system indicating that a new periodicity arises below T/sub p/. The cylindrical AMRO can be restored by high magnetic field or high pressure thus confirming the re-entrance into the high-temperature state. We present the results on the low temperature AMRO in all the three salts and analyze them in view of possible changes in the electronic system. Other peculiarities of both the semiclassical MR and quantum oscillations are also discussed within the proposed model.

Hall effect in organic conductor (ET)/sub 2/TlHg(SCN)/sub 4/

Summary form only given. The temperature dependence of Hall constant has been studied in the organic quasi - two dimensional conductor (ET)/sub 2/TlHg(SCN)/sub 4/ in interval 1.8 - 20K. The sign of Hall constant corresponds to holes in this temperature area. At temperature decreasing from 12K up to 5K Hall voltage rapidly increases approximately 20 times. Such behaviour is connected with the phase transition in SDW state. But quantitive change of Hall constant is not in agreement with the zone structure calculations.

Structure and transport properties of the first et salt with metal complex anion containing selenocyanate ligand, (ET)/sub 2/TlHg(SeCN)/sub 4/

Summary form only given. Synthesis and structure of the quasi two-dimensional organic salt /spl alpha/-(ET)/sub 2/TlHg(SeCN)/sub 4/ are reported. Distinctions of the bond length distributions in three crystallographically independent ET molecules have been found, which may result in some charge localization in the radical-cation layer. Temperature dependencies of the resistivity in various crystallographic directions have been studied. It has been shown that in the /spl alpha/-(ET)/sub 2/TlHg(SeCN)/sub 4/ salt there is no the low-temperature phase transition into a spin density wave state, characteristic of the /spl alpha/-(ET)/sub 2/TlHg(SeCN)/sub 4/ compounds with M=K, Tl and Rb. The strong Shubnikov-de Haas oscillations have been observed in the magnetic fields up to 36 T and at temperatures down to 0.1 K. Detailed comparison of the structure as well as the electrical and the magnetotrasport properties of this compound to its thiocyanate analog, /spl alpha/-(ET)/sub 2/TlHg(SeCN)/sub 4/ is discussed.

Suppression of insulating state in (BETS)/sub 2/FeCl/sub 4/ by magnetic field

Summary form only given. Electrical and magnetotransport properties of the first organic conductor (BETS)/sub 2/FeCl/sub 4/ (BETS = bis(ethylenedithio)tetraselenafulvalene) with magneticions Fe/sup 3+/ are reported. It has been revealed that the sharp metal-insulator phase transition at 8 K, which is driven by the antiferromagnetic interaction between the Fe/sup 3+/ ions in this compound at ambient pressure, is suppressed by the magnetic field H /spl ges/ 10 T. This unusual phenomenon is connected with a plausible ferromagnetic ordering of the Fe/sup 3+/ ions momentums, which is induced by the field. It could result in some kind of evaporation of the previously condensed conduction electrons into a high conductivity state. Temperature-magnetic field (T - H) phase diagram is presented.

The partial substitution effects of br-anions for other halide anions (Cl, I) in the superconductor ET/sub 2/CuN(CN)/sub 2/Br

Summary form only given. By means of partial substitution of Br with Cl- or I-anions the mixed salts of ET/sub 2/CuN(CN)/sub 2/Br/sub 1-x/Hal/sub x/ (Hal = Cl, I) have been synthesized. The conducting properties of these salts have been studied. A new phase, /spl kappa/ET/sub 2/CuN (CN) /sub 2/Br/sub 0.5/Cl/sub 0.5/, which is a superconductor with T/sub c/=11.3 K, was found in the ET/sub 2/Cu(CN)/sub 2/Cl/sub x/Br/sub 1-x/ system. This superconductor is more three dimensional than pure bromide salt. The partial substitution of Br for I-anions leads to formation of mixed salts with the properties like those of pure iodide. However, in contrast to a latter, the salt ET/sub 2/CuN(CN)/sub 2/Br/sub 1-x/I/sub x/ (x = 0.1-0.15), exhibits superconducting transition with T/sub c/=3.5 K under pressure of about 0.3 kbar.