Browsing by Subject "Superconducting transition temperature"

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Open Access
Different behaviour of magnetic impurities in crystalline and amorphous states of superconductors
(Institute of Physics, 2002) Park, M.-A.; Savran, K.; Kim, Y.-J.
It has been observed that the effect of magnetic impurities in a superconductor is drastically different depending on whether the host superconductor is in the crystalline or the amorphous state. Based on the recent theory of Kim and Overhauser (KO), it is shown that as the system is getting disordered, the initial slope of the Tc depression is decreasing by a factor √ℓ/ξ0, when the mean free path ℓ becomes smaller than the BCS coherence length ξ0, which is in agreement with experimental findings. In addition, for a superconductor in a crystalline state in the presence of magnetic impurities the superconducting transition temperature Tc drops sharply from about 50% of Tc0 (for a pure system) to zero near the critical impurity concentration. This pure limit behaviour was indeed found by Roden and Zimmermeyer in crystalline Cd. Recently, Porto and Parpia have also found the same pure limit behaviour in superfluid He-3 in aerogel, which may be understood within the framework of the KO theory.
Open Access
Possibility of superconductivity of two-dimensional electrons on the surface of liquid heliuM, films
(Pergamon Press, 1993) Tanatar, Bilal; Hakioǧlu T.
We consider the possibility of superconductivity in a system of two-dimensional electrons on the surface of liquid helium films. Taking into account of the interaction between electrons and the surface excitations of liquid helium films-ripplons, within the weak coupling BCS theory, we estimate the superconducting transition temperature for various interaction strengths, film thicknesses, and electron densities. The superconducting transition temperature Tc, under experimentally realizable conditions, is calculated to be a few mK's. © 1993.
Open Access
Temperature dependence of the phase of the response of YBCO edge-transition bolometers: effects of superconductivity transition and thermal parameters
(Institute of Physics Publishing, 2003) Fardmanesh, M.; Askerzade, İ. N.
The variation of the phase of the response of YBCO edge-transition bolometers on crystalline MgO substrate is found to be dependent on the normal-superconducting transition. The phase of the response for T < Tc increased at low modulation frequencies where the thermal diffusion length into the sample substrate from the top absorbing YBCO film is longer than the substrate thickness. The substrate/cold-head boundary resistance mainly dominates the thermal conductance of our samples at low frequencies. This transition-dependent change of the phase of the response is interpreted to be due to the effects of the order parameter of the YBCO material on the phonon spectrum and hence the determining Kapitza boundary resistance. The phase of the response decreased at high modulation frequencies where the thermal diffusion length into the substrate is less than the substrate thickness. The results of our analytical model for the low modulation frequencies agree well with the measured values for temperatures close to the Tc-zero.