Browsing by Author "Schwenk, Helmut"
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Item Open Access α- and β-(BEDT-TTF)2I3 - two modifications with contrasting groundstate properties: insulator and volume superconductor(1985) Schwenk, Helmut; Gross, Frieder; Heidmann, Claus Peter; Andres, Klaus; Schweitzer, Dieter; Keller, Heimo J.The α-modification of (BEDT-TTF)2I3 undergoes a metal-to-insulator transition at T = 135 K. Application of hydrostatic pressure shifts the transition temperature to lower values. Above 12 kbar semimetallic behavior is observed, but no superconductivity is detected up to a pressure of 17 kbar and temperatures down to l00 mK. The β-modifcation, on the other hand, exhibits ambient pressure volume superconductivity below Tc = 1.05 K. Measurements of the anisotropy of the diamagnetic shielding- as well as the Meissner-magnetization are presented.Item Open Access Determination of the electron phonon coupling and the superconducting gap in β-(BEDT-TTF)2X crystals (X=I3, IAuI)(1987) Nowack, Andreas; Poppe, Ulrich; Weger, Meir; Schweitzer, Dieter; Schwenk, HelmutWe performed point-contact and tunneling measurements on the organic superconductors beta-(BEDT-TTF)2I3 and beta-(BEDT-TTF)2IAuI, in the normal and superconducting states. The point-contact measurement in the normal state provides the Eliashberg function alpha2(omega)F (omega). This function has maxima at 4 and 15 mV, as well as a sharp peak at 1 mV which seems to indicate a very soft phonon strongly coupled to the electrons. The measurements in the superconducting state provide the superconducting gap, which for the tunneling measurements has a value 2Delta/kB Tc=4, just slightly above the BCS value.Item Open Access Magnetic-field–induced transition and quantum oscillations in tetramethyltetraselenafulvalenium perrhenate, (TMTSF)2ReO4(1986) Schwenk, Helmut; Parkin, Stuart S. P.; Schumaker, Robert R.; Greene, Richard L.; Schweitzer, DieterWe report magnetoresistance measurements in (TMTSF)2ReO4 which give evidence for a magnetic-field–induced transition. We also find Shubnikov–de Haas oscillations above and below the field-induced transition-a result not explained by recent theories of this novel transition.Item Open Access New, organic, volume superconductor at ambient pressure(1985) Schwenk, Helmut; Heidmann, Claus Peter; Gross, Frieder; Hess, Edgar; Andres, Klaus; Schweitzer, Dieter; Keller, Heimo J.We have observed volume superconductivity in β-(BEDT-TTF)2I3 (β-bis-ethylenedithiolo-tetrathiafulvalene-triiodide) at ambient pressure with a diamagnetic transition temperature of 1.03±0.02 K.