Josephson Vortices in High Tc Superconductors

Abstract

When a magnetic field is applied to the type-II superconductors in a superconducting state, the magnetic field penetrates into the superconductors above the first critical field Hc1, and is quantized in a unit of 0 (=h/2e=2.07x 10-7gauss.cm2). This is a general view of magnetic flux (vortex) in the type-II superconductors as schematically drawn in Fig.1 (a). The wave function of superconductivity  extends to the coherence length , and the applied magnetic field H is screened by the supercurrent in a range of the penetration depth of  from the center of vortex core. In this case, vortex has a core of normal state. In a lower magnetic field, vortices behave as isolated vortices. When the magnetic field becomes higher, interaction between/among vortices, vortices form „Abrikosov“ vortex lattice in triangular or square distribution, which has been observed by scanning tunneling microscope (Hess et al. 1994) and small angle neutron scattering (Yethiraj et al, 1993) mainly in mettalic and intermetallic superconductors.