Temperature-bias noise and quantum shot noise as probes of pairing symmetry in iron pnictides

Quantum noise has long served as a powerful probe of quantum transport in mesoscopic junctions. Recently, temperature-driven noise, or ΔT noise, has attracted growing interest due to its presence even in the absence of average charge current. In this work, we investigate a normal metal–insulator–iron-pnictide junction and demonstrate how zero-temperature quantum shot noise, finite-temperature quantum noise, and ΔT noise can discriminate between s++ and s+− pairing symmetries, which are relevant to iron-based superconductors. We introduce ΔT noise as a novel probe for distinguishing between the two pairing symmetries. In contrast to conductance, which exhibits a single peak for both s++ and s+− states with only a difference in magnitude, the ΔT noise reveals qualitatively distinct features: a twin-peak structure for the s++ pairing symmetry and a single-peak profile for the s+− state. A similar symmetry-dependent contrast is observed in both zero-temperature quantum shot noise and finite-temperature quantum noise, where the s++ state consistently exhibits a twin-peak structure, while the s+− state shows a single-peak response. Our results demonstrate that noise-based measurements form a mutually reinforcing set of probes that enables reliable identification of superconducting gap symmetry in iron-pnictide superconductors.