Fluctuation contributions to the heat capacity of superconducting thin films
Zally, George Daniel
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https://hdl.handle.net/2142/25854
Description
Title
Fluctuation contributions to the heat capacity of superconducting thin films
Author(s)
Zally, George Daniel
Issue Date
1970
Doctoral Committee Chair(s)
Mochel, J.M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
fluctuation contributions
heat capacity
superconducting thin films
Language
en
Abstract
"This thesis is a report of experimental investigations into the
nature of the phase transition of a two-dimensional superconductor between
its normal and superconducting states. The heat capacity and electrical
resistivity have been measured for a series of amorphous Bismuth-Antimony
films of various thicknesses.
Mean field theories predict a discontinuous jump in heat capacity
at the transition, and this has ""been observed in experiments on pure bulk
superconductors. The presence of thermodynamic fluctuations causes a breakdown
of mean field theory if one gets close enough to the transition
temperature, T. For a pure bulk superconductor, the temperature region
over which thermodynamic fluctuations become important is inuneasurably
small.
For dirty superconductors in restricted geometries (i.e., films
or filaments), fluctuations are important over a much wider range in temperature.
Various experimentalists have measured the electrical conductivity
of thin films and have observed an extra fluctuation conductivity above Tc
which varies as (T - Tc )-1 as the transition temperature is approached.
A number of theorists have treated fluctuation effects to first order and
have calculated the fluctuation conductivity, finding the (T - Tc )-1 depenc
dence and even producing the observed magnitude. Similar calculations
applied to the heat capacity of a dirty thin film superconductor predict
an extra fluctuation heat capacity above T that varies as (T - Tc )-1 and
is important over the same temperature range as is the fluctuation
conductivity.
For the amorphous thin films examined in this experiment, the
electrical conductivity measured was in agreement with theory and with
other experiments. The heat capacity measurements showed an extra contribution
that was consistent with the (T - Tc)-1 behavior predicted. The
width in temperature of the heat capacity transition was approximately the
same as for the resistive transition.
A recent calculation by Masker, Marcelja, and Parks, treating
fluctuations to second order, predicts a sharp peak in heat capacity just
below T. Such an effect should have been observable with the resolution
c
of the present experiment, but no such peak was seen."
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