Critical field

Critical field

Upper critical field

The upper critical field is the magnetic field (usually expressed in teslas (T)) which completely suppresses superconductivity in a Type II superconductor at 0K (absolute zero).

More properly, the UCF is a function of temperature (and pressure) and if these are not specified absolute zero and standard pressure are implied.

Werthamer–Helfand–Hohenberg theory predicts the upper critical field (Hc2) at 0 K from Tc and the slope of Hc2 at Tc.

The UCF (at 0 K) can also be estimated from the coherence length(ξ) using the Ginzburg-Landau expression : Hc2 = 2.07 x 10-15 Tm2/(2 Pi ξ2) [1]

Articles on superconductivity use Hc2 or Bc2 interchangeably since the materials are rarely magnetic.

Lower critical field

The magnetic field at which the magnetic flux starts to penetrate a type-2 superconductor at 0 K (absolute zero).

References

  1. ^ Introduction to Solid State Physics, Charles Kittel, John Wiley and Sons, Inc.

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