Abstract: has been measured between 4.2 K and 0.3 K in fields up to 3.4 Tesla. The data can be described by variable-range hopping (VRH) in a magnetic field and by postulating a second transport mechanism independent of the magnetic field. A model based on orbital shrinking of the localized wavefunction (positive MR) and on a Zeeman shift of the energy levels (negative MR) can be fit to the data and yields the Bohr radius and the binding energy of the localized states as well as the variation of the density of states at the Fermi level, which in most samples is found to be quadratic. The magnetoresistance (MR) of heavily doped (CH)x We have studied the dc conductivity of heavily doped polyacetylene (IASF-) at temperatures between 4.2 K and 0.3 K and in magnetic fields up to 3.4 Tesla. From the MR in particular it is possible to obtain detailed information on the transport mechanism. 3’ 6 Our samples were polymerized by the Stuttgart group. Iodine doping was performed in Regensburg by exposing the samples to iodine vapor and consecutive vacuum pumping. The magnetic field was oriented parallel to the polyacetylene films and to the current. Typical results are shown in Figs. 1 and 2 where the relative change of the resistance as a function of the magnetic field is displayed at various constant temperatures. At high temperatures (Fig. 1 ) the MR is negative but upon cool-down continuously changes to positive values (Fig. 2). At the lowest temperatures the p o s i 1 tive M R is similar to our earlier data on less metallic samples , the differences being the two orders of magnitude smaller values 173 D o w n l o a d e d B y : [ G e r m a n N a t i o n a l L i c e n c e 2 0 0 7 ] A t : 1 3 : 3 5 2 0 D e c e m b e r 2 0 1 0 1 74 E. ETTLINOER. W. OSE AND W. SCHOEPE I . I 0 10 20 3D B (ledal 12
Publication Year: 2010
Publication Date: 2010-01-01
Language: en
Type: article
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Cited By Count: 12
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