Critical surface
Superconductors - Theoretical basis

The critical quantities T_c, B * = µ₀ H * and J_c are interdependent and form a surface, the so-called critical surface in (T, B, J ) space (figure 17, page 9). The critical surface delimits the non-dissipative state from the dissipative state, and not the superconducting state from the normal state, not least because of the definitions of the critical current density and the irreversibility field. When the critical current is exceeded, vortices move, but the material is still considered to be in the superconducting state, even though it is dissipating energy.

The critical surface can be modified by mechanical stress or deformation.

Finally, for certain...