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  • 1990-1994  (1)
  • 1985-1989  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Non-ohmic conduction in doped polyacetylene at low temperatures (1986)
    Springer
    The European physical journal 64 (1986), S. 19-23 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electrical conductivity of a iodine-doped polyacetylene is measured as a function of the electric field ℰ at temperatures between 4K and 0.3K. We find that after an initial non-linear behavior σ increases linearly with ℰ in agreement with a theoretical description based on variable-range hopping conduction. The non-linear rise at low fields depends on the iodine concentration. In heavily doped samples the increase is small and varies as ℰ2, whereas in less conductive samples a large change is observed at 0.3K which varies approximately as log ℰ for fields from 1 V/m to 150 V/m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313684
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Static and dynamic forces on a permanent magnet levitating between superconducting surfaces (1993)
    Springer
    Journal of low temperature physics 93 (1993), S. 85-100 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A charged magnetic microsphere (radius 100 µm) is levitating inside a superconducting niobium capacitor. Because of its charge of about 1 pC, oscillations about the equilibrium position can be excited and detected electrically. The properties of this oscillator are investigated in order to study the static and dynamic forces of magnetic levitation. We find resonance frequencies between 200 Hz and 600 Hz. The resonance frequency and the damping are amplitude dependent due to nonlinear return forces and nonlinear friction, respectively. At small amplitudes the Q value is about 106 in vacuum. A dc field can be applied to change the equilibrium position and consequently the resonance frequency. From the data the spatial dependence of the static force and of the dynamic stiffness can be determined and an empirical relation between both is established. Quite often, we find a hysteretic behavior of the static force whereas the stiffness is a reversible function of the position. Amplitude dependent damping is observed both in the decay of the free oscillations and in the dependence of the amplitude of the forced oscillations on the driving force.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00682282
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Variable-range hopping conduction in doped germanium at very low temperatures and high magnetic fields (1988)
    Springer
    The European physical journal 71 (1988), S. 455-463 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The conductivity of doped Ge below the metal-insulator transition is measured at temperatures between 4 K and 40 mK and in magnetic fields up to 7 Tesla. In zero field the resistivity exponent diverges asT −1/2. In weak fields the magnetoresistance increases asB 2 and becomes exponentially large in strong fields and at low temperatures. The results can be described quantitatively in terms of variable-range hopping between localized states having a Coulomb gap in the density of states at the Fermi level. The magnetoresistance is calculated for arbitrary fields by means of a quasi-classical method. A fit to the data gives the radius of the localized states and the density of states. The sample is found to be very close to the metal-insulator transition. A small increase of the binding energy is observed in strong fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313932
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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