Critical magnetic field

A critical magnetic field is the magnitude of the magnetic field that destroys superconductivity .

Superconductors are characterized not only by the absence of electrical resistance, but also by the Meissner effect , which consists in pushing the magnetic field beyond the limits of the superconductor. For a given temperature, the Meissner effect is manifested only for fields smaller than critical. Fields larger than the critical field penetrate the superconductor and destroy superconductivity.

Critical magnetic field $H_{c}$ ${\ displaystyle H_ {c}}$ $H_ {c}$ connected with the difference of free energies of the normal and superconducting phases:

{\frac {H_{c}^{2}}{8\pi }}=F_{n}-F_{s}

{\ displaystyle {\ frac {H_ {c} ^ {2}} {8 \ pi}} = F_ {n} -F_ {s}}

{\ displaystyle {\ frac {H_ {c} ^ {2}} {8 \ pi}} = F_ {n} -F_ {s}}

Its temperature dependence is well described by the empirical formula

H_{c}(T)=H_{c}(0)[1-(T/T_{c})^{2}]

{\ displaystyle H_ {c} (T) = H_ {c} (0) [1- (T / T_ {c}) ^ {2}]}

{\ displaystyle H_ {c} (T) = H_ {c} (0) [1- (T / T_ {c}) ^ {2}]}

,

Where $T_{c}$ ${\ displaystyle T_ {c}}$ $T_ {c}$ - critical temperature .

Superconductors of the second kind are characterized by two critical fields - $H_{c1}$ ${\ displaystyle H_ {c1}}$ ${\ displaystyle H_ {c1}}$ and $H_{c2}$ ${\ displaystyle H_ {c2}}$ ${\ displaystyle H_ {c2}}$ . With an external magnetic field $H<H_{c1}$ ${\ displaystyle H <H_ {c1}}$ ${\ displaystyle H <H_ {c1}}$ Meissner effect is observed. In the range of fields $H_{c1}<H<H_{c2}$ ${\ displaystyle H_ {c1} <H <H_ {c2}}$ ${\ displaystyle H_ {c1} <H <H_ {c2}}$ a mixed state arises - a magnetic field penetrates into the superconductor in the form of quantized vortices . With the magnitude of the magnetic field $H>H_{c2}$ ${\ displaystyle H> H_ {c2}}$ ${\ displaystyle H> H_ {c2}}$ superconductors of the second kind also go into a normal state.

Literature

Schmidt V.V. Introduction to the physics of superconductors. M., "MCCMO", 2000.
Critical magnetic field // Physical Encyclopedia : [in 5 vol.] / Ch. ed. A.M. Prokhorov . - M .: Soviet Encyclopedia, 1990. - T. 2: Q-factor - Magnetooptics. - 704 s. - 100,000 copies. - ISBN 5-85270-061-4 .
Superconductivity // Physical Encyclopedia : [in 5 vols.] / Ch. ed. A.M. Prokhorov . - M .: Great Russian Encyclopedia, 1994. - T. 4: Poynting - Robertson - Streamers. - 704 s. - 40,000 copies. - ISBN 5-85270-087-8 .

Critical magnetic field

Literature

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