Geometric edge barrier in the Shubnikov phase of type II superconductors

Abstract

In type II superconductors the magnetic response

can be irreversible due to two different reasons: vortex pinning and barriers for flux

penetration. Even without bulk pinning and in absence of a microscopic Bean-Livingston

surface barrier for vortex penetration, superconductors of nonellipsoidal shape can exhibit

a large geometric barrier for flux penetration. This edge barrier and the resulting

irreversible magnetization loops and flux-density profiles are computed from continuum

electrodynamics for superconductor strips and disks with constant thickness, both without

and with bulk pinning. Expressions are given for the field of first flux entry Hen and for

the reversibility field Hrev above which the pin-free magnetization becomes reversible.

Both fields are proportional to the lower critical field Hc1 but else depend only on the

specimen shape. These results for rectangular cross section are compared with the well

known reversible magnetic behavior of ideal ellipsoids.