Browsing by Author "Heidmann, Claus Peter"
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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 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.Item Open Access Observation of the Meissner effect in the high-Tc (pressure-)phase of the organic superconductor β-(BEDT-TTF)2I3(1985) Veith, Helmut; Heidmann, Claus Peter; Gross, Frieder; Lerf, Anton; Andres, Klaus; Schweitzer, DieterIt is shown that the recently found superconducting state below 6 K in β-(BEDT-TTF)2I3 under a pressure of 1.5 kbar is diamagnetic and exhibits Meissner effects of up to 24 %, indicating that superconductivity is a true volume effect in these crystals. In contrast, no traces of diamagnetism are found in iodine doped α-(BEDT-TTF)2I3, for which resistively observed superconducting transitions in the vicinity of 3 to 5 K have also been reported.Item Open Access Temperature and angular dependence of the upper critical field in β-(BEDT-TTF)2I3 and its deuterated analogue(1986) Heidmann, Claus Peter; Andres, Klaus; Schweitzer, DieterWe present measurements of the temperature and angular dependence of the upper critical fields of β-ET2I3 and d-β-ET2I3. The data are analyzed in terms of an anisotropic effective mass model. The results of cooling rate experiments are reported and the effect of deuteration on superconductivity is discussed.Item Open Access Temperature and pressure dependence of the resistivity of β-(BEDT-TTF)2X (X=I3, I2Au) and αt-(BEDT-TTF)2I3(1988) Weger, Meir; Bender, Klaus; Klutz, Thomas; Schweitzer, Dieter; Gross, Frieder; Heidmann, Claus Peter; Probst, Christian; Andres, KlausThe temperature dependence of the resistivity of the organic metals and superconductors {β-(BEDT-TTF)2I3, β-{3-(BEDT-TTF)2I2Au and αt(BEDT-TTF)2I3 was measured at ambient and at several isotropic pressures (up to 2.5 kbar). By the application of a relatively low pressure, it is possible to measure the term in the resistivity that is linear in temperature. This term is masked by the larger T2 term at ambient pressure. It is shown that in the temperature range below 120 K, the external modes are mainly responsible for the resistivity, while above this temperature the flipping of the CH2 groups becomes important. The linear electron-phonon coupling corresponds to a value of λ between 1 and 1.5.