Physics Group - II (3110018)

BE | Semester-1   Winter-2019 | 02-01-2020

Q5) (b)

Explain London's penetration depth.

  • Maxwell’s equations could not explain the zero resistance and perfect diamagnetism observed as main characteristics of superconductivity.
  • F. London and H. London (London brothers) suggested that motion of superconducting electrons in the presence of applied electric field E.
  • If a magnetic field is applied to a superconductor which is initially in zero field, the magnetic field is a function of time.
  • The potential decay of magnetic field at the interior surface of superconductor.
  • Mathematical expression for the Hall voltage is given by:

           Bx = B0 e- xλ

           Where, B0 = magnetic field at the surface 
           Where, x = distance inside the superconductor from surface
           Where, λL = Penetration depth

  • The potential decay of magnetic field at the interior surface of superconductor.
  • λL is the distance across which the magnetic field becomes  ' e '  times weaker.
  • λL can be formulated as:

           λL = mμ0 n q2

           Where, m = charge carrier of mass 
           Where, n = number of density
           Where, μ0 = absolute permeability