$Δ_T$ Noise in Mesoscopic Hybrid Junctions: Influence of Barrier Strength and Thermal Bias
Quantum noise is a fundamental probe of quantum transport phenomena, offering insights into current correlations and wave-particle duality. A particularly intriguing form of such noise, $Δ_T$ noise, emerges under a finite temperature difference in the absence of charge current at zero voltage bias. In this work, we investigate $Δ_T$ noise in mesoscopic hybrid junctions incorporating insulating barriers, where the average charge current remains zero at zero bias. Using quantum shot noise measurements, we demonstrate that $Δ_T$ noise in metal-insulator-superconductor (NIS) junctions is approximately $16$ times greater than in metal-insulator-metal (NIN) counterparts. Our analysis further reveals that $Δ_T$ noise exhibits a non-monotonic dependence on barrier strength, rising to a peak before declining, while increasing monotonically with the applied temperature bias. These findings underscore the rich interplay between thermal gradients and barrier properties in determining quantum noise characteristics in hybrid mesoscopic systems.