Fluctuation heat capacity of amorphous Nb3Ge films

N. A.H.K. Rao, Allen M Goldman

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The temperature dependencies of the heat capacities of amorphous Nb3Ge films have been measured near the superconducting transition using ac calorimetry. From an analysis of data both above and below, but outside, the transition region, a transition temperature TBCS was uniquely determined. The departure of the measured heat capacity from the BCS theory below the transition and from the usual sum of lattice and electronic terms above was then extracted. Above TBCS, over a substantial temperature range, the departure could be attributed to fluctuations and could be fit with a two-dimensional free fluctuation theory modified to take into account the fact that film thicknesses, which were on the order of 1000 », were not always small in comparison with the temperature-dependent coherence length. However, the transition temperature obtained from such a fit was always found to be higher than TBCS determined from data outside the transition region. Furthermore, below TBCS a broad bump in the excess heat capacity was observed. A quantitative description of the excess heat capacity data may require the development of a theory based on the two-component Ginzburg-Landau model which treats the quartic term in a more realistic manner than in the Hartree model, and which takes into account both thickness corrections in films with a small natural ξ(0) and the possibility of quenched or frozen-in disorder.

Original languageEnglish (US)
Pages (from-to)253-276
Number of pages24
JournalJournal of Low Temperature Physics
Issue number3-4
StatePublished - Feb 1 1981

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