quasisuperconducting

Quasisuperconducting is an informal term used to describe materials or systems that display transport and magnetic properties reminiscent of superconductivity without achieving true superconductivity. In quasisuperconducting regimes, electrical resistance can become extremely small at low temperatures, and there may be a partial diamagnetic response, but a finite resistance or incomplete Meissner effect remains under practical current densities or applied fields.

Common contexts include inhomogeneous or nanostructured materials where superconducting regions form a percolating network yet lack global phase coherence, and in ultra-thin films where thermal phase fluctuations suppress long-range order. The concept also appears in discussions of proximity-coupled heterostructures, where superconducting correlations extend into non-superconducting layers but do not constitute bulk superconductivity.

Within theory, quasisuperconductivity is attributed to limited phase stiffness, strong fluctuations, disorder, or finite-size effects that prevent a true superconducting phase transition. Experimental signatures include a sharp drop in resistance over a limited temperature range with a nonzero residual resistance at low temperature, and a diamagnetic signal that is weaker than a full Meissner response. AC impedance measurements may show finite loss, and critical current and fields can be markedly reduced compared with true superconductors.

While not universally recognized as a distinct thermodynamic phase, the label serves to describe a regime where superconducting-like phenomena dominate transport properties without full superconductivity, helping to study fluctuation phenomena and nanoscale inhomogeneity.

See also: superconductivity; fluctuation phenomena; percolation theory; proximity effect; mesoscopic physics.