Negative Spin $Δ_T$ noise Induced by Spin-Flip Scattering and Andreev Reflection

• URL: http://arxiv.org/abs/2307.14072v4
• Date: Sat, 23 Aug 2025 16:54:42 GMT
• Title: Negative Spin $Δ_T$ noise Induced by Spin-Flip Scattering and Andreev Reflection
• Authors: Sachiraj Mishra, Colin Benjamin,
• Abstract summary: We study charge $Delta_T$ noise and spin $Delta_T$ noise in a superconducting junction.<n>While charge $Delta_T$ noise remains strictly positive, spin $Delta_T$ noise undergoes a sign reversal from positive to negative.
• Score: 0.0
• License: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Abstract: We study charge $\Delta_T$ noise, followed by an examination of spin $\Delta_T$ 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 $\Delta_T$ noise remains strictly positive, spin $\Delta_T$ 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 valid for spin quantum shot noise also. The emergence of negative spin $\Delta_T$ noise has two major implications. First, it establishes a clear distinction between spin resolved $\Delta_T$ 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 $\Delta_T$ 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 $\Delta_T$ 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 $\Delta_T$ noise and highlights their role as distinctive fingerprints of spin-dependent scattering in superconducting hybrid devices.

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