Hc2 (0)=-0.69Tc (dHc2/dT)Tc
In the above equation why does the value 0.69 comes up.
WHH stands for Werthamer, Helfand and Hohenberg who developed a well-known theory of Hc2. The particular formula you are interested in was derived by Maki, de Gennes and others in 1964. The value 0.69 comes from the equation for Hc2 in the dirty limit (see, e.g. the text around Eq. 8.26 in de-Gennes book, Superconductivity of metals and alloys)
WHH stands for Werthamer, Helfand and Hohenberg who developed a well-known theory of Hc2. The particular formula you are interested in was derived by Maki, de Gennes and others in 1964. The value 0.69 comes from the equation for Hc2 in the dirty limit (see, e.g. the text around Eq. 8.26 in de-Gennes book, Superconductivity of metals and alloys)
The theory by Werthamer-Helfand-Hohenberg (WHH) predicts the universal behavior of the upper critical field Hc2 ( T ) in superconductors with weak electron-phonon coupling. The behavior can be described by a universal function hc2 (T ) expressed in the reduced variables for magnetic field h=H/[Tc(-dHc2 /dT)] and temperature t=T/Tc.
The function hc2(t) has a negative second derivative and saturates to the value hc2 ~0.7 at t=0. The WHH theory has described successfully properties of conventional supercon- ductors but many new superconductors discovered during the last decade exhibit behavior inconsistent with the theory.
A nice paper of temperature dependence of Hc2 is:
http://www.issp.ac.ru/lek/gantmakher/art97RE.pdf
Could you please tell me which equation is exactly used for fitting WHH model to the upper critical field versus temperature data.
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