Dino Schweitzer

Non-linear transport in /spl alpha/-(BEDT-TTF)/sub 2/I/sub 3/

Summary form only given. The two-dimensional organic conductor /spl alpha/-(BEDT-TTF)/sub 2/I/sub 3/ undergoes a metal-insulator phase transition of unknown origin at T/sub MI/ = 135 K. We studied the electrodynamic response of /spl alpha/-(BEDT-TTF)/sub 2/I/sub 3/ in a extremely wide range of frequency, covering microwave and millimetel wave frequencies as well as the optical spectral range, and find a frequency dependent conductivity up to 1000 cm/sup -1/ in the low temperature phase. This is accompanied be a non-linear transport with a smooth onset at about 10 V/cm. Our X-ray studies show no indication of superstructure reflections and clearly rule out the formation of a charge density wave ground state. The lack of a temperature dependence in the millimeter wave conductivity between 20 K and 100 K makes hopping transport unlikely. There also is experimental evidence against the simple concept of a spin density wave.

Electronic properties of the superconductor (BEDO-TTF)/sub 2/ReO/sub 4/(H/sub 2/O)

Summary form only given. The electronic properties of the organic superconductor (BEDO-TTF)/sub 2/ReO/sub 4/(H/sub 2/O) were investigated by temperature dependent resistivity, FT - IR reflectivity, ESR, Hall effect and magnetoresistance measurements. Shubnikov de Haas (SdH) oscillations were observed in magnetic fields up to 24 T in the temperature range 0.5 K to 4.2 K. The electronic band structure was calculated by employing the extended Huckel tight binding method on the basis of its room temperature crystal structure. The two observed SdH frequencies of 76 and 37 Tesla correspond very well with two cross-sectional areas of the Fermi surface obtained for a hole and an electron pocket from the tight binding calculations. From the temperature dependence of the SdH oscillation amplitudes the cyclotron effective mass (m*) belonging to the larger pocket was found to be 0.9m/sub 0/, while for the smaller pocket m*=1.15m/*sub 0/. Measurements of the angular dependence of the SdH frequencies show no deviation from that expected for a cylindrical Fermi - surface. The plasma frequency /spl omega//sub p/ is determined by fitting a Drude modell to the FT - JR reflection data. The bandwidth derived from /spl omega//sub p/ corresponds well to the band structure calculation.