London penetration depth
In superconductors, the London penetration depth (usually denoted as or ) characterizes the typical distance to which a magnetic field penetrates into a superconductor.[1] Typical values of range from 50 to 500 nm.
The London pentration depth results from considering the London equation and Ampère's circuital law.[1] If one considers a superconducting medium occupying , and weak external magnetic field applied along -direction in the empty space , then inside the superconductor the magnetic field is given by
i.e. is the distance across which magnetic field becomes times weaker. The form of is found by this method to be
- ,[1]
for charge carriers of mass , number density and charge .
The penetration depth is determined by the superfluid density which is an important quantity determines Tc in high-temperature superconductors. If some superconductors have some node in their energy gap, the penetration depth at 0 K depends on magnetic field because superfluid density is changed by magnetic field and vice versa. So, accurate and precise measurements of the absolute value of penetration depth at 0 K are very important to understand the mechanism of high-temperature superconductivity.
London penetration depth can be measured by muon spin spectroscopy when the superconductor doesn't have an intrinsic magnetic constitution. The penetration depth is directly converted from the depolarization rate of muon spin in relation which
Further reading
References
See also
- London equations 1935
- Ginzburg-Landau theory 1950