ArXiv · 2023
We study charge Δ_T noise, followed by an examination of spin Δ_T noise, in the normal metal-spin flipper-normal metal-insulator-superconductor (N-sf-N-I-S) junction. Our analysis reveals a key contrast: while charge Δ_T noise remains strictly positive, spin Δ_T noise undergoes a sign reversal from positive to negative, driven by the interplay between spin-flip scattering as well as Andreev reflection. In contrast, charge quantum shot noise remains positive and sign-definite, which is also valid for spin quantum shot noise. The emergence of negative spin Δ_T noise has two major implications. First, it establishes a clear distinction between spin-resolved Δ_T noise and quantum shot noise: the former is dominated by opposite-spin correlations, whereas the latter is led by same-spin correlations. Second, it provides access to scattering mechanisms that are not captured by quantum shot noise alone. Thus, negative spin Δ_T noise serves as a unique probe of the cooperative effects of Andreev reflection and spin flipping. We further place our results in context by comparing them with earlier reports of negative Δ_T noise in strongly correlated systems, such as fractional quantum Hall states, and in multiterminal hybrid superconducting junctions. Overall, this work offers new insights into the mechanisms governing sign reversals in Δ_T noise and highlights their role as distinctive fingerprints of spin-dependent scattering in superconducting hybrid devices.
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