Critical magnetic fields of superconducting tungsten
Black, William Carter
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https://hdl.handle.net/2142/25694
Description
Title
Critical magnetic fields of superconducting tungsten
Author(s)
Black, William Carter
Issue Date
1967
Doctoral Committee Chair(s)
Wheatley, J.C.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
critical magnetic fields
superconducting tungsten
parabolic dependence
resistivity
Language
en
Abstract
The thermodynamic critical field curve of a superconducting
tungsten specimen with resistivity ratio 7,500 has
been measured as a function of temperature down to 3 m K (1 m K -
10-3 oK). From the raw data the critical field H0 at T = 0 is
found to be 1.14·1 ± .007 G, and the zero field transition temperature
Tc is 15.39 + .17 mOK. The normal-state electronic specific
heat parameter y, as derived from the critical field data, is
0.87 + .04 mJ/mole °K2. However, the magnetic field at the
specimen is slightly altered by the nearby paramagnetic refrigerant-
thermometer. An estimated correction applied to the data
gives
the new values Ho = 1.148 +/- .010 G, Tc = 15.37 +/- .17 moK, and gamma
= 0.90 ± .06 mJ/mole °K2, which are considered to be the
most probable values of these parameters for the tungsten specimen
studied here. Deviation of the measured critical field
from a parabolic dependence on temperature is in good agreement
with the weak-coupling BCS theory. The very small calculated
Ginzburg-Landau parameter (x:: 2 X 10^-3 ) and extremely large calculated
coherence length (~o ~ 32u) are favorable for observation
of a large supercooling effect in tungsten at temperatures well
below Tc. Assuming that the ideal critical supercooling field
was observed on an electropolished specimen, the experimental
value for u is (2.6 ± 1.6) X 10^-3. A large and reproducible,
though less than ideal, superheating effect was also observed with
this same electropolished specimen.
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