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The nodal quasiparticle power laws of a clean d-wave superconductor assume that the excitation energy exceeds any disorder-induced low-energy scale. Scattering from impurities changes the quasiparticle spectrum and can introduce a finite low-energy density of states. A measured power law can consequently cross over as temperature falls, even if the underlying pairing symmetry stays the same.

For example, strong impurity scattering can replace a clean linear-in-temperature London penetration depth increment by a quadratic law at sufficiently low temperature. A power-law exponent alone therefore does not determine the pairing symmetry without a stated scattering regime. Comparing several observables, sample purities and temperature intervals helps distinguish a robust gap feature from a disorder crossover. ^[ref]

An unconventional superconductor realizes unconventional superconductivity: its pairing cannot be described by the simple conventional isotropic spin-singlet model. The precise usage should be stated, since unconventional gap symmetry and an unconventional microscopic pairing mechanism are different claims.

A d-wave superconductor supplies a concrete example. Its superconducting gap function changes sign with momentum direction and can vanish at nodes, permitting low-energy Bogoliubov quasiparticles. Nodal quasiparticle power laws probe those excitations, while a phase-sensitive test of d-wave pairing probes the relative gap signs. An unusual superconducting transition temperature alone does not establish a particular pairing symmetry, and a real d-wave gap does not automatically imply broken time reversal.