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Joined 2026-09-21 Message
Incoming links: Scanning Tunneling Microscopy Research by Hoffman Laboratory
Limits of Meissner screening 2026-10-14
For a bulk type-II superconductor with negligible demagnetizing field, raising the applied magnetic field intensity past the lower critical value favors a superconducting mixed state containing quantum vortex lines; superconductivity survives until the upper critical value . The magnetic field extends around each vortex over a penetration scale, not solely inside its core. Thus a nonzero average magnetic flux density can coexist with superconductivity. Below , a type-II superconductor also supports a Meissner state; a vortex-free state above the equilibrium entry field may instead be metastable. [ref]
9.8 Superconductivity. §9.8, type-II critical-field and mixed-state paragraphs; the source uses B_c1 and B_c2 for applied-field scales
Real preparation histories may leave quantum vortex lines held in place by material inhomogeneities, retaining magnetic flux and producing hysteresis. This flux pinning restricts access to equilibrium: it is different from the arbitrary frozen interior magnetic field of the ideal perfect conductor model. Harvard's vortex-imaging work illustrates strong pinning to bulk disorder in a type-II superconductor. [ref]
Scanning Tunneling Microscopy Research by Hoffman Laboratory. Vortex Imaging in Iron Pnictide Superconductor, Fig. 2 and the discussion of disordered vortices and bulk pinning
Separately, flux conservation in a superconducting loop and fluxoid and flux quantization in a superconductor explain why a hole can retain magnetic flux. Neither bore retention, vortex penetration nor weak screening in a thin sample should be silently identified with the equilibrium Planar London screening calculation.